NEW: Britain's Foreign Office warns against travel to Yemen
- Sources say al Qaeda in final planning stages of unspecified plot
- 21 U.S. embassies and consulates to close Sunday
- The State Department issues a global travel alert on possible al Qaeda attacks
(CNN) -- A global travel alert issued Friday by the State Department said al Qaeda may launch attacks in the Middle East, North Africa and beyond in coming weeks, and the U.S. government prepared to close embassies and consulates in the region Sunday as a precaution.
The steps showed the heightened concerns about what U.S. officials said was intelligence in recent days that indicated a potential attack emanating from al Qaeda in Yemen.
Britain's Foreign Office warned against travel to Yemen and advised British citizens to leave the country, while a senior Yemeni national security official told CNN that the government was "on high alert against possible attacks in the days to come."
"The threat appears much worse than it has in a long time," the Yemeni official said.
According to three sources, the United States has information that al Qaeda in Yemen was in the final stages of planning for an unspecified attack.
One of the sources said the preparations appeared to have increased in recent days with the approaching end of the Muslim holy month of Ramadan, while a U.S. official noted it was unclear whether the plot would be directed at a target inside Yemen or elsewhere.
"Current information suggests that al Qaeda 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 State Department travel alert said.
U.S. officials who spoke to CNN on condition of not being identified said intelligence agencies have been tracking a growing threat against American and Western targets by al Qaeda's affiliate in Yemen for a few weeks.
In recent days, the officials said, further intelligence indicated a potential attack in Yemen and threats against U.S. interests in the Middle East and North Africa, prompting the Obama administration to issue a public warning and plan to close diplomatic facilities in the region Sunday.
Based on the intelligence, officials said, there was particular concern about the U.S. Embassy in Yemen between Saturday and Tuesday, which fall in the final days of Ramadan. In particular, Sunday is Lylet al-Qadr, the Night of Power in Islamic teachings and one of the holiest of the year.
"This is a higher-than-normal threat stream," one official told CNN, and a senior U.S. official said there was "more than the usual chatter" about potential terror threats, which was not specific about time and location.
Embassies and consulates closing
A State Department list made public Friday showed the 21 embassies and consulates that will close Sunday, normally the start of the work week in the countries affected.
They included embassies in Iraq, Egypt, Libya, Saudi Arabia, Afghanistan, Yemen and 11 other countries, as well as consulates in Iraq, Saudi Arabia and the United Arab Emirates.
Other embassies to be closed were in the United Arab Emirates, Algeria, Jordan, Djibouti, Bangladesh, Qatar, Kuwait, Bahrain, Oman, Mauritania and Sudan.
A senior State Department official said the embassies and consulates could be kept closed for additional days. Embassies and consulates in the region are for the most part closed or operate with minimal staff on Fridays and Saturdays.
The U.S. Embassy in Israel also will be closed as normal on Sunday.
President Barack Obama was briefed on the closures, a U.S. official told CNN on condition of not being identified.
House Democratic leader Nancy Pelosi told reporters that House leadership also had been briefed on the situation, and that the travel alert and embassy closings provided "some understanding of the seriousness of the threat."
Rep. Ed Royce told CNN's "New Day" on Friday that al Qaeda was linked to a terror threat that prompted the embassy closings.
"It's my understanding that it is al Qaeda-linked, all right, and the threat emanates in the Middle East and in Central Asia," said Royce, a California Republican who chairs the House Foreign Affairs Committee.
Obama met with Yemeni President Abdo Rabu Mansour Hadi at the White House on Thursday. Yemen has been cracking down on al Qaeda.
Biden briefed legislators
Earlier this week, Vice President Joe Biden and senior State Department officials went to Congress to discuss embassy security after last year's terrorist attack on a U.S. diplomatic compound in Benghazi, Libya, that killed four Americans, including Ambassador Christopher Stevens.
Biden also briefed congressional leadership, key committee chairs and ranking members about the latest threat concerns, a source who attended the meeting said.
Another official said the recent intelligence might not have warranted such a response before the Benghazi attack, which created a political firestorm for the Obama administration.
On Thursday, State Department spokeswoman Marie Harf said the agency was taking the steps at diplomatic sites out of an abundance of caution