The top US intelligence official, Dennis Blair, has said that the global economic crisis is the main security concern facing America.
The director of national intelligence said at least a quarter of countries had experienced some instability because of the worldwide downturn.
Giving evidence to senators, he also said he believed al-Qaeda's leadership had been weakened over the past year.
But he pointed to Afghanistan and Pakistan as areas of concern.
Afghan security had deteriorated and Pakistan had to gain control of its border region before the situation would improve, Mr Blair said in an annual assessment of national threats.
Iran, he added, was at the very least keeping open the option of developing nuclear weapons but North Korea was unlikely to use nuclear weapons unless its government felt its survival was at stake.
Risk of instability
"The primary near-term security concern of the United States is the global economic crisis and its geopolitical implications," Mr Blair told a senate panel.
"Economic crises increase the risk of regime-threatening instability if they persist over a one- to two-year period."
Warning of the dangers of protectionism, he said that perceptions that the global crisis had originated in the US could make it difficult for America to maintain its lead in promoting free trade.
The intelligence chief warned that al-Qaeda, the militant network which claimed the 9/11 attacks, was still planning attacks on the West, and appeared to view Europe as a "viable launching-point".
But blows to the militants in Pakistan and Iraq meant they were "less capable and effective" than a year ago.