The United States issued an extraordinary global travel warning to Americans about the threat of an al-Qaida attack and closed down 21 embassies and consulates across the Muslim world for the weekend.

The alert was the first of its kind since an announcement preceding the 10th anniversary of the Sept. 11, 2001, terrorist attacks.

A Sept. 11 attack last year on a U.S. diplomatic post in Benghazi, Libya, killed the ambassador and three other Americans.

“There is a significant threat stream, and we’re reacting to it,” said Gen. Martin Dempsey, chairman of the Joint Chiefs of Staff. He told ABC in an interview to be aired Sunday that the threat was “more specific” than previous ones and the “intent is to attack Western, not just U.S. interests.”

The warning said al-Qaida or its allies might target either U.S. government or private American interests. The alert expires on Aug. 31.

The New York Times reported Friday night that American officials said the U.S. had intercepted electronic communications among senior operatives of al-Qaida.

The State Department said the potential for terrorism was particularly acute in the Middle East and North Africa, with a possible attack occurring on or coming from the Arabian Peninsula.

U.S. officials pointed specifically to Yemen, the home of al-Qaida’s most dangerous offshoot and the network blamed for several notable terrorist plots on the United States.

“Current information suggests that al-Qaida and affiliated organisations 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,” a department statement said.

The State Department urged U.S. travellers to take extra precautions overseas, citing potential dangers involved with public transportation systems and other prime sites for tourists. It noted that previous terrorist attacks have cantered on subway and rail networks as well as airplanes and boats.

The alert was posted a day after the U.S. announced it would shut many diplomatic facilities Sunday. Spokeswoman Marie Harf said some missions may stay closed for longer than a day.

Sunday is a business day in Muslim countries, and the diplomatic offices affected stretch from Mauritania in northwest Africa to Afghanistan.

Although the warning coincided with “Al-Quds Day,” the last Friday of the Islamic month of Ramadan when people in Iran and some Arab countries express their solidarity with the Palestinians and their opposition to Israel, U.S. officials played down any connection.

They said the threat wasn’t directed toward a specific U.S. diplomatic facility.

The concern by American officials over the Yemen-based al-Qaida in the Arabian Peninsula is not new, given the terror branch’s gains in territory and reach during Yemen’s prolonged Arab Spring-related instability.

The group made significant territorial gains last year, capturing towns and cities in the south amid a power struggle in the capital that ended with the resignation of Yemen’s longtime leader, Ali Abdullah Saleh. A U.S.—aided counteroffensive by the government has since pushed the militants back.

Yemen’s current president, Abdo Rabby Mansour Hadi met U.S. President Barack Obama at the White House on Thursday, where both leaders cited strong counterterrorism cooperation. Earlier this week, Yemen’s military reported a U.S. drone strike killed six alleged al-Qaida militants in the group’s southern strongholds.

As recently as June, the group’s commander, Qasim al-Rimi, released an Arabic-language video urging attacks on U.S. targets and praising the ethnic Chechen brothers accused of carrying out the deadly Boston Marathon bombings in April.

“The blinking red intelligence appears to be pointing toward an al-Qaida in the Arabian Peninsula plot,” said Seth Jones, counterterror expert at the Rand Corp.

Britain also took action Friday in Yemen, announcing it would close its embassy there on Sunday and Monday as a precaution.

Britain, which closely coordinates on intelligence matters with Washington, stopped short of releasing a similar region-wide alert but added that some embassy staff in Yemen had been withdrawn “due to security concerns.” British embassies and consulates elsewhere in the Middle East were to remain open.

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