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. From left, FBI Director Robert Mueller, Director of National Intelligence James Clapper, and CIA Director David Petraeus take their seats on Capitol Hill in Washington, Tuesday, Jan. 31, 2012, prior to testifying before the Senate Intelligence Committee hearing to assess current and future national security threats. 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.