WASHINGTON -- A worldwide alert has been issued for all U.S. citizens traveling abroad due to an unspecified al Qaeda threat, State Department officials warned Friday.
The terror group and their affiliated organizations "may focus efforts to conduct attacks in the period between now and the end of August," a statement said.
"U.S. citizens should take every precaution to be aware of their surroundings and to adopt appropriate safety measures to protect themselves when traveling," it added. " The Department of State alerts U.S. citizens to the continued potential for terrorist attacks, particularly in the Middle East and North Africa, and possibly occurring in or emanating from the Arabian Peninsula."
The travel alert expires on August 31.
The warning came as officials announced that the United States is working with foreign spy agencies to try to find out more about the target of a suspected al Qaeda-linked plot to attack any of the 284 American diplomatic posts around the world, according to U.S. officials.
The 22 embassies and consulates that normally open on Sundays -- mostly in the Muslim world -- were closing this weekend because of the potential threat.
But the intelligence received to date about the supposed plot says nothing about a specific target, according to the officials. U.S. officials told NBC News that the threat warning is based primarily on a "significant increase in chatter from a growing number of intercepts" throughout the region.
The closures so far include the larger diplomatic missions in Cairo, Tel Aviv, Riyadh, Baghdad, Kabul, Bahrain and dozens of other embassies and consulates.
"It is possible we may have additional days of closings as well, depending on our analysis,” a State Department official said.
House Foreign Affairs Chairman Ed Royce (R-Calif.) said Friday that the threat was “al Qaeda-linked.”
“The basis is to protect our personnel. It's a step that I support, I believe the Secretary of State is correct in his judgment that in an abundance of caution we should protect our personnel on the ground,” he said. "The decision on Sunday to close these embassies is based upon information that indicates that we have a clear and ongoing threat."
Terrorism analyst Roger Cressey told NBC's TODAY that the end of the holy month of Ramadan on Wednesday was a significant time for Muslims and might heighten the risk of attack by extremists.
“Certainly the intelligence community and the State Department are going to pay even closer attention to the threat environment right now," he said.
On Thursday, a senior State Department official said “we have instructed all U.S. Embassies and Consulates that would have normally been open on Sunday to suspend operations, specifically on August 4th.”
State Department spokeswoman Marie Harf said the U.S. has been "apprised of information .... that indicates we should institute these precautionary steps.”
She said the steps were being taken "out of an abundance of caution and care for our employees and others who may be visiting our installations."
Notices on several embassies’ websites pointed to a “Worldwide Caution” issued by the State Department on Feb. 19 for further information.
The embassies and consulates due to close Sunday include: Algiers, Algeria; Sana'a, Yemen; Tel Aviv, Israel; Riyadh, Saudi Arabia; Dhaka, Bangladesh; Kuwait City, Kuwait; Ankara, Turkey; Muscat, Oman; Doha, Qatar; Khartoum, Sudan; Cairo, Egypt; Kabul, Afghanistan; Baghdad, Iraq; Amman, Jordan; Abu Dhabi, United Arab Emirates; Manama, Bahrain; Tripoli, Libya; Nouakchott, Mauritania; and Doha, Qatar.
Terrorism expert Xenia Dormandy, U.S. director of London-based think tank Chatham House, said it was the first time in memory that the U.S. had closed such a large number of embassies at once.
“This is the first time I’ve seen this,” she said. “The bottom line is clearly they’ve had firm intelligence from multiple sources that there’s an al Qaeda threat or an al Qaeda-affiliated threat," she said.
Dormandy said the United States' actions were likely influenced by the attack on the U.S. Consulate in Benghazi, Libya, in September in which Ambassador Christopher Stevens and three other Americans were killed.
“I think they are being cautious because any attack on American diplomats is something they want to avoid at all costs," she added. "I think they are certainly likely to be more nervous now about making a mistake than they were before the Libyan [Benghazi consulate] attack, but they’ve seen the consequences of what can happen if you don’t take precautions, so it’s perhaps an appropriate response."
Another U.S. official said "half" of the caution is "because of Benghazi."