Under the cover of darkness and high security, the United States has now evacuated almost all of its personnel from Yemen on an Air Force C-17.
A senior U.S. official said Ayman al Zawahiri, somewhere in Pakistan, directed the head of al Qaeda in Yemen to carry out a "big attack" with "strategic significance."
Yemen's Nasir al Wuhayshi is one of the known terrorists behind the underwear bomb and surgically implanted explosives, small bombs placed inside the human body.
"This group is fairly ingenious, fairly bold, and eager to cause damage," Daniel Benjamin, coordinator for counterterrorism with the State Department, said.
U.S. intelligence officials intercepted communications between the two al Qaeda leaders. That prompted the wave of embassy closures throughout the Middle East, Africa, and South Asia over the weekend.
The initial target is believed to be the U.S. Embassy in Yemen, but other American and Western facilities could also be on the target list.
Intelligence officials believe trucks have been packed with explosives to carry out the attack in Yemen. A search for the trucks has already begun.
"Yemen, of course, is a country that doesn't have a very strong central government and there's been lots of territory for the group to operate in and to use as a safe haven," Benjamin said.
A drone strike targeting al Qaeda members was reported in Yemen overnight--the fourth this past week. Yemeni officials say the drone fired a missile at a car carrying four men, setting it on fire and killing them.
The government of Yemen has criticized the U.S. and British governments for evacuating embassy staff, saying it "serves the interests of the extremists."
The U.S. Ambassador to Yemen is already back in Washington, D.C., and it's unlikely he will return to the Middle East any time soon.