WASHINGTON (AP) - Al-Qaida is in decline around the world but is still a leading threat to the United States, joined by others like Iran, the top U.S. intelligence official said Tuesday in an annual report to Congress on threats facing America. Iran's leaders seem prepared to attack U.S. interests overseas, particularly if they feel threatened by possible U.S. action, Director of National Intelligence Jim Clapper told the Senate Intelligence Committee. But Clapper, CIA chief David Petraeus and others reasserted their stance that Iran is not building nuclear weapons, in contrast to Israeli officials' statements that Iran could have nuclear capability within a year. Petraeus said he met with the head of Israel's intelligence agency, Mossad, last week to discuss Israel's concerns, but he did not say whether Israel agreed with the U.S. assessment that Iran had not yet decided to make a nuclear weapon. Israeli Defense Minister Ehud Barak said last week that Iran is proceeding toward nuclear weapons capability and time is "urgently running out." Al-Qaida and Iran are part of a mosaic of interconnected enemies the U.S. faces, including terrorists, criminals and foreign powers, who may try to strike via nuclear weapons or cyberspace, Clapper and the others said. Al-Qaida still aspires to strike the U.S., but it will likely have to go for "smaller, simpler attacks" as its ranks are thinned by continued pressure from U.S. drone strikes and special operations raids since Osama bin Laden's death at the hands of Navy SEALs in Pakistan last year, Clapper predicted. "When you take one two and three out in a single year," that weakens the force, added Petraeus. The CIA chief pointed out that "four of the top 20 in a single week were captured or killed," last year, leaving the leadership struggling to replace itself. The intelligence chiefs predicted al-Qaida's regional affiliates will try to pick up the slack for the beleaguered core group in Pakistan - from the Yemeni offshoot al-Qaida in the Arabian Peninsula to Somalia's al-Shabaab. If they can't reach the U.S. homeland, they'll try to attack western targets in their geographic areas, they said, and the Yemeni branch of al-Qaida remains the most likely affiliate to try to attack the U.S. homeland. The U.S. continues to put pressure on the Yemeni offshoot, and on Monday mounted airstrikes targeting al-Qaida leaders there, killing at least four suspected militants, according to Yemeni and military officials. U.S. officials also said there's been no decision on whether to trade five dangerous Taliban prisoners now being held in Guantanamo, as part of nascent peace talks with the Taliban. Clapper said the White House would first have to determine where they would be held, and how they would be watched after being released to make sure they did not return to militancy. Sen. Saxby Chambliss, R-Ga., said the five men the Taliban have named are considered too dangerous to release by U.S. counterterrorist authorities, but Petraeus said his agency had run several possible scenarios to figure out how best to free them. Just below al-Qaida on the list of threats comes the possibility of proliferation of weapons of mass destruction, from chemical and biological, to nuclear and radiological. The intelligence community does not believe states that possess them have supplied them to terror groups, but that remains a risk. Iran has the technical ability to build a nuclear weapon, Clapper said. If Iran moves to enrich uranium beyond the current level of 20 percent, to a weapons grade level, it would be a sign Iran had decided to move ahead, Petreaus added. Citing last year's thwarted Iranian plot to kill the Saudi ambassador in the U.S., "some Iranian officials - probably including Supreme Leader Ali Khamenei ... are now more willing to conduct an attack in the United States in response to real or perceived U.S. actions that threaten the regime," Clapper said. The North Korean nuclear weapons program is a continued threat to global security, though the program is intended for self-defense, his assessment states: "We judge that North Korea would consider using nuclear weapons only under narrow circumstances" and "probably would not attempt to use nuclear weapons against U.S. forces or territory, unless it perceived its regime to be on the verge of military defeat and risked an irretrievable loss of control." China and Russia remain the key threats to the U.S. in cyber-space, with "entities" in both countries "responsible for extensive illicit intrusions into US computer networks and theft of US intellectual property," though Iran is also a player, Clapper said. He warned of growing cyber-espionage by foreign governments against U.S. government and businesses, and said many such intrusions are not being detected. "They seem most interested in our technology," he said. "If they can steal it from us, that works to their benefit" so they don't have to spend their own money on research. Insider threats are another category of risk, in which disgruntled employees like accused Army soldier Bradley Manning allegedly leak information to the public or sell it to competing corporations or nations. The annual threat assessment looked further afield to places like Afghanistan, where it assessed the Afghan government's progress as fragile, and the Taliban as "resilient." The group is less able to intimidate the Afghan population that last year, especially in areas where NATO forces are concentrated, but its leaders continue to direct the insurgency from their safe haven in Pakistan, the report said. AP writer Eileen Sullivan contributed to this report from Washington, D.C. AP intelligence writer Kimberly Dozier can be followed on Twitter (at) kimberlydozier.