Updated

Al-Qaida is in decline around the world but is still a leading threat to the United States, the top U.S. intelligence official said Tuesday in an annual report to Congress on threats facing the country.

Director of National Intelligence Jim Clapper also told the Senate Intelligence Committee that Iran's leaders seem prepared to attack U.S. interests overseas, particularly if they feel threatened by possible U.S. action.

The U. S. now faces many interconnected enemies, including terrorists, criminals and foreign powers, who may try to strike via nuclear weapons or cyberspace, with the movement's Yemeni offshoot and "lone wolf" terror attacks posing key threats, he said.

But while al-Qaida still aspires to strike the U.S., 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.

"We judge that al-Qaida's losses are so substantial and its operating environment so restricted that a new group of leaders, even if they could be found, would have difficulty integrating into the organization and compensating for mounting losses," Clapper said.

The intelligence community predicts that al-Qaida's regional affiliates — from the Yemeni offshoot al-Qaida in the Arabian Peninsula to Somalia's al-Shabaab — will "surpass the remnants of core al-Qaida in Pakistan," and try to attack "Western targets in its operating area." The Yemeni branch of al-Qaida remains the most likely affiliate to try to attack the U.S. homeland, he added.

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.

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 — but simply hasn't decided to yet, Clapper said.

"We assess Iran is keeping open the option to develop nuclear weapons, in part by developing various nuclear capabilities that better position it to produce such weapons," Clapper said.

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.

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.

The continent of Africa got one of the grimmest reviews. Africa remains "vulnerable to political crises, democratic backsliding, and natural disasters." Violence, corruption and terrorism are likely to plague Africa in areas key to U.S. interests, the review said, with unresolved discord between Sudan and South Sudan, continued fighting in Somalia, and extremist attacks in Nigeria.