WASHINGTON—The deadly attack earlier this month at a U.S. consulate in Libya was "deliberate and organized," the top U.S. spy's office said Friday. 
 
 The revised assessment by the Director of National Intelligence, the office that heads up the various U.S. spy agencies including the Central Intelligence Agency, is the most declarative U.S. statement yet that the Sept. 11 assault on U.S. diplomatic sites in Benghazi, Libya—which left four Americans dead, including U.S. Ambassador Christopher Stevens—was a coordinated terrorist attack. It contrasts with some early administration statements that the siege grew out of a spontaneous protest over an anti-Islam video. 
 
 Enlarge Image Close Associated Press The U.S. Consulate in Benghazi, Libya, after the attack there on Sept. 11, which U.S. intelligence officials now say was a coordinated terrorist strike. 
 
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 The DNI underscored Friday that its latest assessment reflects an evolution in the information emerging from investigations into the attack. The assessment also doesn't yet answer the question at the heart of a growing political controversy: whether the assault was a premeditated attack that the administration should have known about. 
 
 Some Republican critics have implied that the Obama administration knew that the attack was preplanned by terrorist groups but hid that fact to avoid exposing security failures. White House officials say that isn't the case and that they have conveyed what facts they knew at the time. 
 
 The U.S. has ramped up its probe. The CIA has sent operatives to Libya to assist with it, according to a former U.S. official. 
 
 The chain of events that began when protesters stormed the U.S. Embassy in Cairo, and ended with the four Americans' deaths in a succession of firefights in eastern Libya, have posed an unexpected challenge to President Barack Obama's foreign policy record just weeks before the November election. 
 
 How the Attack Unfolded View Graphics 
 
 Evidence shortly after the attacks had "led us to assess that the attack began spontaneously following protests earlier that day at our embassy in Cairo," DNI spokesman Shawn Turner said Friday. 
 
 "As we learned more about the attack, we revised our initial assessment to reflect new information indicating that it was a deliberate and organized terrorist attack carried out by extremists," Mr. Turner said. 
 
 It still isn't clear, he added, "if any group or person exercised overall command and control of the attack, and if extremist group leaders directed their members to participate." He added that "some of those involved were linked to groups affiliated with, or sympathetic to al Qaeda." 
 
 Republicans have accused the White House of conveying mixed messages. 
 
 "I think it's increasingly clear—if now not definitively pointed out—that this was a terrorist attack against our diplomats," Republican nominee Mitt Romney told reporters Friday. "There was a great deal of confusion about that from the very beginning on the part of the administration, and whether that was something that they were trying to paper over or whether it was just confusion given the uncertain intelligence reports—time will tell." 
 
 In the first days after the attack, top administration officials said it was too early to say what precipitated it. Five days after, the U.S. ambassador to the United Nations, Susan Rice, blamed the assault mainly on an anti-Islamic video circulating on the Internet. 
 
 On Sept. 19, however, the top U.S. counterterrorism official said the assault had connections to terrorists, including al Qaeda's North African affiliate. After that, more administration officials, including White House Press Secretary Jay Carney, Defense Secretary Leon Panetta and Secretary of State Hillary Clinton, have labeled it a terrorist attack. President Obama indirectly referred to the assault as an act of "terror" on Sept. 12 but has refrained from using the term since. 
 
 Rep. Peter King (R., N.Y.), a frequent administration critic, called Friday for Ms. Rice's resignation for misleading the public about the nature of the attack. 
 
 Mr. Turner of the DNI's office said intelligence officials provided public officials with "evolving" information about the attacks, beginning with the early assessments. 
 
 "We provided that initial assessment to executive branch officials and members of Congress, who used that information to discuss the attack publicly and provide updates as they became available," he said. "Throughout our investigation, we continued to emphasize that information gathered was preliminary and evolving." 
 
 Friday's statement was an effort to explain "early reports are often wrong or incomplete," he said. "But our intelligence community continues to work around the clock to gather details and understand exactly what happened in Benghazi." 
 
 Still unanswered is whether the attack was planned in advance. In recent days, a consensus among intelligence officials has emerged that the assault was highly organized and involved al Qaeda's affiliate in North Africa, but that the specific attack was planned on the fly on the day of world-wide protests against American installations. 
 
 "The attack's execution was not necessarily indicative of extensive planning," Mr. Turner said, saying there still were "unanswered questions." 
 
 "The degree to which there was some level of planning is one we continue to look at," he said. 
 
 Republicans in Congress, adding to the political pressure, said they have received briefings that counter the White House version of events and indicate the attacks had been "preplanned." 
 
 Eight Republicans wrote to Mr. Obama this week to voice frustration that the administration has left many unanswered questions about the attack. A bipartisan group of senators, including Senate Foreign Relations Committee Chairman John Kerry (D., Mass.), is also requesting more information from the administration. 
 
 The crime scene in Benghazi, abandoned after the U.S. evacuation and subject to looters for days, has posed security problems for the U.S. investigators. However, a U.S. law-enforcement official played down the value of the site, given that it is tainted more than two weeks after the attack. Federal agents are using intelligence and analyzing intercepts, and some are doing interviews in Tripoli. 
 
 Intelligence agencies have stepped up their reporting on Libyan terror groups, said a congressional aide, who said shortly after the attacks the counterterrorism-related U.S. intelligence reports on Libya increased at least fivefold. 
 
 —Julian E. Barnes and Evan Perez contributed to this article. 
 
 Write to Siobhan Gorman at siobhan.gorman@wsj.com and Carol E. Lee at carol.lee@wsj.com ||||| WASHINGTON — The Obama administration’s shifting accounts of the fatal attack on the American diplomatic compound in Benghazi, Libya, have left President Obama suddenly exposed on national security and foreign policy, a field where he had enjoyed a seemingly unassailable advantage over Mitt Romney in the presidential race. 
 
 After first describing the attack as a spontaneous demonstration run amok, administration officials now describe it as a terrorist act with possible involvement by Al Qaeda. The changing accounts prompted the spokesman for the nation’s top intelligence official, James R. Clapper Jr., to issue a statement on Friday acknowledging that American intelligence agencies “revised our initial assessment to reflect new information indicating that it was a deliberate and organized terrorist attack carried out by extremists.” 
 
 The unusual statement was not solicited by the White House, according to Shawn Turner, the spokesman for Mr. Clapper, the director of national intelligence, but it seemed calculated to relieve some of the pressure on the White House for the contradictory accounts given in the two and a half weeks since the attack. It is unlikely to stop questions from the Romney campaign, which senses an opportunity. 
 
 “This incident is a hinge event in the campaign because it opens up the opportunity to talk more broadly about Obama’s foreign policy,” said Richard S. Williamson, a former diplomat and an adviser to Mr. Romney. 
 
 But the questions are likely to come not just from partisan Republicans. The Benghazi attack calls into question the accuracy of intelligence-gathering and whether vulnerable American personnel overseas are receiving adequate protection. Even allies of the president like Senator John Kerry, a Massachusetts Democrat and the chairman of the Senate Foreign Relations Committee, have petitioned the White House for more information about how the government protects diplomatic installations abroad. 
 
 Almost since the smoke cleared in Benghazi, Republicans have accused Mr. Obama’s aides of deliberately playing down the attack. Senator John McCain, Republican of Arizona, condemned the administration’s initial account of the attack as “disgraceful,” saying on CBS that it “shows a fundamental misunderstanding not only of warfare, but of what’s going on in that part of the world.” 
 
 The White House maintains that its account changed as intelligence agencies gathered more details about the attack, not from any desire to diminish its gravity. Mr. Obama, his aides point out, labeled the assault an “act of terror” in his first public response, in the Rose Garden, a day after it happened. 
 
 “In any situation like this, you know more one week later than you did the day after, and more two weeks later than you did one week after,” said Benjamin J. Rhodes, a deputy national security adviser. “Given the demand for information, we feel there is a responsibility to provide the facts as we understand them.” 
 
 For the White House, the latest intelligence is helpful in one regard: It indicates that the attack, while carried out in an organized manner, mainly by a local extremist group in eastern Libya, Ansar al-Shariah, was probably not planned months or weeks in advance. 
 
 After poring over intercepted electronic communications, informant reports and photographs and video from the scene, American intelligence and counterterrorism officials have concluded that a small number of the local Libyan militia members probably have ties to Al Qaeda in the Islamic Maghreb, the Qaeda affiliate in North Africa. But analysts say they have not found any evidence to indicate that the affiliate ordered or planned the attack. 
 
 In his statement, Mr. Turner said that it was unclear who had directed the attack, but that “we do assess that some of those involved were linked to groups affiliated with, or sympathetic to, Al Qaeda.” 
 
 At the same time, further details about the attack could lay bare lapses in security that could damage the administration. CNN has reported, from a diary belonging to J. Christopher Stevens, the American ambassador killed in the attack, that he harbored worries about his security. Mr. Williamson, who served as special envoy to Sudan under President George W. Bush, said it was unlikely that Mr. Stevens would not have relayed those concerns to the State Department. 
 
 Mr. Romney has been cautious in his public comments about the attack since his initial response, which was criticized by Mr. Obama and Republicans for being premature and unseemly in the face of a tragedy. But Mr. Romney has singled out the administration for its conflicting accounts, and has begun questioning whether it heeded warnings of anti-American attacks in the region, timed to the anniversary of the terrorist attacks on Sept. 11, 2001. ||||| The office of the nation’s spy chief, James R. Clapper Jr., issued a statement Friday defending the Obama administration’s accounts of the siege of U.S. missions in Libya. (Chip Somodevilla/Getty Images) 
 
 The office of the nation’s spy chief issued a statement Friday defending the Obama administration’s accounts of the siege on a U.S. mission in Libya, saying it became clear only in the aftermath that it was “a deliberate and organized terrorist attack.” 
 
 The statement appeared aimed at quieting criticism, mostly from Republicans, of the administration’s shifting characterizations of a Sept. 11 assault that killed the U.S. ambassador to Libya and three other Americans. Officials initially described the attack as spontaneous but in recent days have said it was an act of terrorism with links to al-Qaeda. 
 
 The release from the office of Director of National Intelligence James R. Clapper Jr. came as lawmakers sought more details about the siege in Benghazi. The Senate Foreign Relations Committee sent a letter to the State Department on Thursday posing questions about intelligence in the period leading up to the attack and the adequacy of the security at U.S. compounds. 
 
 Shawn Turner, a spokesman for Clapper, said U.S. agencies have altered their assessments based on intelligence that has emerged through an ongoing investigation. 
 
 “In the immediate aftermath, there was information that led us to assess that the attack began spontaneously following protests earlier that day at our embassy in Cairo,” Turner said. That information was conveyed to administration officials as well as members of Congress. 
 
 1 of 35 Full Screen Autoplay Close Skip Ad × Anti-U.S. protests across the globe View Photos The protests that started outside the U.S. Embassy in Cairo have spread as far as India. Caption The protests that started outside the U.S. Embassy in Cairo have spread as far as India. Sept. 24, 2012 Muslim demonstrators hold their shoes up to a portrait of Florida pastor Terry Jones during a protest against the anti-Islamic You Tube video in Quetta, Pakistan. More than 50 people have died around the world in violence linked to the low-budget video, which mocks Islam and the prophet Muhammad, since the first demonstrations erupted in Cairo on Sept. 11. Banaras Khan/AFP/Getty Images Buy Photo Wait 1 second to continue. 
 
 But analysts have since “revised our initial assessments to reflect new information indicating that it was a deliberate and organized terrorist attack carried out by extremists,” Turner said. “Some of those involved were linked to groups affiliated with, or sympathetic to al-Qaeda.” 
 
 The release marks a rare instance in which the intelligence director’s office has weighed in through a public statement on details of an event overseas, let alone one that remains under investigation during a presidential campaign. In an e-mail, Turner indicated that the director’s office, while seeking to stay out of the political fray, became convinced that it should clarify the intelligence community’s position. 
 
 “I put out the message because I think it’s important that people understand that early reports are often wrong or incomplete, but our intelligence community continues to work around the clock to gather details and understand exactly what happened in Benghazi,” Turner said. 
 
 The evolving intelligence picture may explain why administration officials — including Susan E. Rice, ambassador to the United Nations — seemed adamant early on that the attack was part of a spontaneous protest triggered by an anti-Islamic video produced in the United States. It wasn’t until Sept. 20 that the head of the National Counterterrorism Center described the assault as a terrorist attack — a description echoed by Secretary of State Hillary Rodham Clinton this week. 
 
 Republicans have accused the administration of seeking to play down terrorist links at a time when President Obama has emphasized the degradation of al-Qaeda as a signature foreign policy success. 
 
 Sen. John F. Kerry (D-Mass.), chairman of the Foreign Relations Committee and an administration ally, has deflected Republican demands that the State Department submit a report on the attack to Congress within 30 days. Instead, the panel submitted a letter seeking answers as a State Department review led by former U.S. ambassador Tom Pickering gets underway.
– The nation's spy chief took the unusual step yesterday of issuing a statement to defend the shifting US position on the Libya consulate attack, reports the Washington Post. Yes, said national intelligence director James Clapper, the assault initially seemed to be a spontaneous response to that anti-Islam movie, but we “revised our initial assessments to reflect new information indicating that it was a deliberate and organized terrorist attack carried out by extremists. Some of those involved were linked to groups affiliated with, or sympathetic to al-Qaeda." The New York Times thinks it's an attempt to take pressure off the White House as Republicans zero in on a potential miscue on national security—if it was a planned attack, why didn't we know about it?—and foreign policy. The Wall Street Journal notes that Mitt Romney kept up the pressure yesterday on the campaign trail: "There was a great deal of confusion about that from the very beginning on the part of the administration, and whether that was something that they were trying to paper over or whether it was just confusion given the uncertain intelligence reports—time will tell." Frequent White House critic Peter King called for the resignation of Susan Rice, the US ambassador to the UN, who stated repeatedly in the days after the attack that it was spontaneous. "Somebody has to pay the price for this," the GOP congressman told CNN.