Americans and other foreigners streamed to the airport in Sanaa after the State Department warned of an extremely high threat level. And at the fortified U.S. Embassy, nonessential staffers were ordered to leave, flown out by the U.S. military.

　　But, in Washington, State Department spokeswoman Jen Psaki wouldn't call it an evacuation.

　　JEN PSAKI, State Department: Let me just make clear what this is and what this is not. This is a reduction in staffing. This is -- we still have a presence in Yemen. But -- and we are -- we will continue to evaluate. I don't have any updates on when staff may return.

　　MARGARET WARNER: It was reported that today's order to leave, coming after widespread embassy closings and a worldwide travel alert, was triggered by a communication between al-Qaida's leader, Ayman al-Zawahri, and Nasir al-Wuhayshi, the chief of its affiliate, al-Qaida in the Arabian Peninsula, or AQAP. The Yemeni government objected to today's U.S. order, but did cite specific intercepted threats.

　　RAJEH BADI, Yemeni government spokesman (through interpreter): There were attempts to control key cities in Yemen. The plot was planned by al-Qaida for the 27th day of Ramadan. The aim was to control two important ports by dropping in al-Qaida members wearing military uniforms who would pretend to ask for Ramadan tips owed to them. Then they would attack.

　　MARGARET WARNER: AQAP has tried to mount operations outside Yemen, too, the failed 2009 Christmas Day bomber and the 2010 plot to ship explosives in printer cartridges to the U.S. The U.S. has launched multiple drone strikes in Yemen, including one today that killed four suspected al-Qaida operative.