The United States on Friday issued a worldwide travel alert to all Americans through Aug. 31 due to an unspecified al-Qaeda threat that led to embassy closures.
“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,” it said.
“Current information suggests that al-Qaida and affiliated organizations continue to plan terrorist attacks both in the region and beyond, and that they may focus efforts to conduct attacks in the period between now and the end of August. This Travel Alert expires on August 31, 2013.”
The alert was issued after the U.S. said that all American embassies and consulates that normally open on a Sunday would close on Aug. 4 because of a possible al Qaeda-related threat. A senior State Department official warned they could remain shut for an extended period.
At least 18 diplomatic posts were affected by the closure, with most posting details of the shutdowns on their websites.
The officials said the threat appeared to be related to al-Qaeda and tied to Ramadan, the Muslim month of fasting, which ends Wednesday.
It was aimed at overseas diplomatic posts, not at facilities inside the U.S., they said.
State Department spokeswoman Marie Harf said the U.S. has been "apprised of information that out of an abundance of caution and care for our employees and others who may be visiting our installations, that indicates we should institute these precautionary steps.”
The 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.”
“It is possible we may have additional days of closing as well … The department, when conditions warrant, takes steps like this to balance our continued operations with security and safety,” the official added.
Notices on several embassies’ websites pointed to a “Worldwide Caution” issued by the State Department on Feb. 19 for further information.
“Credible information indicates terrorist groups … seek to continue attacks against U.S. interests in the Middle East and North Africa,” it said. “The U.S. government remains highly concerned about possible attacks against U.S. citizens, facilities, businesses, and perceived U.S. and Western interests.”
Sunday is a normal workday in Muslim countries and Israel.
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; Cairo, Egypt; Kabul, Afghanistan; Baghdad, Iraq; Amman, Jordan; Abu Dhabi, United Arab Emirates; Manama, Bahrain; Tripoli, Libya; Nouakchott, Mauritania; and Doha, Qatar.
Harf, who didn't say which or how many embassies would be closed, did not reveal what kind of information led to the decision.
She said they could be closed for a longer period "depending on our analysis."
Sunday is President Barack Obama's 52nd birthday, and it's also the day Iran inaugurates Hassan Rowhani as its new president.
But U.S. officials told NBC News they had heard nothing to indicate that the date was chosen for either of those reasons.
Ian Johnston, Charlene Gubash and Robert Windrem of NBC News contributed to this report.