Hours before 22 U.S. embassies and consulates were to close for a day, President Barack Obama met with top security leaders Saturday to review the situation that led to the unprecedented move.
A U.S. global travel alert remained in place amid fears that al Qaeda may launch attacks in the Middle East, North Africa and beyond in coming weeks.
The threat prompted the United States to announce that 22 facilities would be closed on Sunday, including in Yemen, which was a focus of concern.
Obama met Saturday with his White House chief of staff, Secretary of State John Kerry, Secretary of Defense Chuck Hagel, as well as the heads of Homeland Security, the National Security Agency, the FBI and CIA, the United Nations and the Joint Chiefs of Staff.
On Saturday, the security around the U.S. embassy in Yemen was even tighter than last year when the embassy was raided by protesters. At least 12 tanks were stationed within 500 meters of the building.
Hundreds of additional security forces were deployed, and roads leading to the embassy were closed. Checkpoints were set up at a distance from the embassy, and trucks weren't allowed to pass anywhere near the main embassy road.
Yemen's special forces, the most elite, were seen in small numbers near the embassy, as well.
Meanwhile, Britain, France and Germany have said they, too, will close their embassies in the Yemeni capital, Sanaa, on Sunday and Monday for security reasons. No other embassies are affected, they said.
Neither Italy nor Spain -- which has no embassy in Yemen -- planned to close any of their embassies.
The U.S. embassies closed on Sunday -- a day they would normally be open -- stretch across a swath of North Africa and the Middle East, from Mauritania to Oman. Bangladesh and Afghanistan, both majority Muslim nations, also are affected.
The U.S. government's actions are in response to growing intelligence that shows a potential for attacks in Yemen and elsewhere in the Middle East and North Africa, said U.S. officials who spoke to CNN on condition of not being identified.
"The threat appears to be much worse than it has (been) in a long time," said a senior national security official in Yemen, where the government is "on high alert against possible attacks in the days to come."
Various Western targets -- not just those tied to the United States -- are under threat, two U.S. officials said.
Three sources said the United States has information that members of al Qaeda in the Arabian Peninsula are in the final stages of planning for an unspecified attack.
One of the sources said such preparations appeared to have increased in recent days with the approaching end of the Muslim holy month of Ramadan. Sunday is Laylet al-Qadr, or the Night of Power, one of the holiest moments on the Muslim calendar.
Said one U.S. official: "It all leads us to believe something could happen in the near future."
Christopher Hill, a former U.S. ambassador to Iraq, told CNN he had never seen embassy closures ordered across such a broad area.
"There have been incidents where they've closed down a number of embassies in the Middle East because the information is not specific enough to say that 'embassy X' got to be closed as opposed to other embassies," said Hill, who joined the U.S. Foreign Service in 1977.
"But I think this, closing all of these embassies in the Middle East to North Africa, is in fact unprecedented. At least, I didn't see this during my career."
'Leave Yemen now'
U.S. officials said that, based on intelligence, they were particularly concerned about the U.S. Embassy in Yemen between Saturday and Tuesday. President Barack Obama, amid regular updates on the situation, has directed officials to take all appropriate steps to protect Americans.
A White House official said the president was updated Saturday morning by Lisa Monaco, his assistant for homeland security and counterterrorism.
Obama, who departed for Joint Base Andrews to play golf, is being updated through the weekend, the official said.
He praised Yemeni President Abdo Rabu Mansour Hadi for his country's efforts following a meeting Thursday at the White House.
The UK Foreign Office has also warned its citizens against travel to Yemen, and urged British nationals to leave as soon as possible.