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WASHINGTON — Top U.S. officials met Saturday to review the threat of a terrorist attack that led to the weekend closure of 21 U.S. embassies and consulates in the Muslim world and a global travel warning to Americans. President Barack Obama was briefed following the session, the White House said.

Obama's national security adviser, Susan Rice, led the meeting and then joined Lisa Monaco, Obama's assistant for homeland security and counter-terrorism, in briefing the president, the White House said in a statement.

"The president has received frequent briefings over the last week on all aspects of the potential threat and our preparedness measures," according to the statement.

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Among those at the meeting Saturday afternoon were the secretaries of state, defense and homeland security and the directors of the FBI, CIA and the National Security Agency, according to the White House. Also attending was Gen. Martin Dempsey, the chairman of the Joint Chiefs of Staff.

In an interview Friday with ABC News, Dempsey said officials had determined there was "a significant threat stream" and that the threat was more specific than previous ones. The "intent is to attack Western, not just U.S. interests," he said.

The global travel warning was the first such alert since an announcement before the 10th anniversary of the terrorist attacks of Sept. 11, 2001.

The warning comes less than a year since the deadly September attack on a U.S. diplomatic post in Benghazi, Libya, and with the Obama administration and Congress determined to prevent any similar breach of an American embassy or consulate.

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

Travelers were advised to sign up for State Department alerts and register with U.S. consulates in the countries they visit.

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

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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. The diplomatic facilities affected stretch from Mauritania in northwest Africa to Afghanistan.

U.S. officials pointed specifically to Yemen, the home of al-Qaida's most dangerous affiliate and the network blamed for several notable plots against the United States, from the foiled Christmas Day 2009 effort to bomb an airliner over Detroit to the explosives-laden parcels intercepted the following year aboard cargo flights.

"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," a department statement said.

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

Rep. Ed Royce, R-Calif., the House Foreign Affairs Committee chairman, said the embassy threat was linked to al-Qaida and concerned the Middle East and Central Asia.

"In this instance, we can take a step to better protect our personnel and, out of an abundance of caution, we should," Royce said. He declined to say if the National Security Agency's much-debated surveillance program helped reveal the threat.