The U.S. Department of State has issued a worldwide travel alert because of a possible al-Qaeda terrorist threat.
It is not clear what that threat might be.
The State Dept. says the potential for terrorism is particularly strong in the Middle East and North Africa. It says an attack could occur or come from the Arabian Peninsula.
The department says in a statement that al-Qaeda and its affiliated organizations "continue to plan terrorist attacks both in the region and beyond."
On Thursday, the State Dept. announced the closures this Sunday of U.S. embassies and consulates in 21 Middle East nations due to an unspecified threat.
The threat was linked to al-Qaeda and focused on the Middle East and Central Asia, said Rep. Ed Royce, R-Calif., chairman of the House Foreign Affairs Committee.
State Department officials said Thursday they were acting out of an "abundance of caution."
Spokeswoman Marie Harf cited information indicating a threat to U.S. facilities overseas and said some diplomatic facilities may stay closed for more than a day.
Sunday is a workday in the Muslim world. American diplomatic missions in Europe, Latin America and many other places are closed on Sunday.
Royce said Friday he supported the State Department decision to "protect our personnel on the ground."