(CNN) - A State Department travel alert Friday said al-Qaida may launch attacks in the Middle East, North Africa and beyond, as the United States is closing 21 embassies and consulates Sunday as a precaution.

The alert says 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. The alert also warns that "terrorists may elect to use a variety of means and weapons and target both official and private interests."

A U.S. official told CNN the embassy closures were because of "more than the usual chatter" about a potential terrorist threat, which was not specific about time and location. It was "directed at American targets overseas," but may not be confined to main diplomatic facilities, the official said.