The United States issued a worldwide travel alert on Friday warning Americans that Al-Qaida may be planning attacks in August, particularly in the Middle East and North Africa.

The State Department travel alert was based on the same intelligence that prompted it to close 21 U.S. embassies and consulates this Sunday, chiefly those in the Muslim world, a U.S. official told Reuters on condition of anonymity. 

"The Department of State alerts U.S. citizens to the continued potential for terrorist attacks, particularly in the Middle East and North Africa, and possibly occurring in or emanating from the Arabian Peninsula," its statement said. 

"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," it added, saying the travel alert would expire on August 31. 

Among the most prominent of Al-Qaida's affiliates is Al-Qaida in the Arabian Peninsula (AQAP), a Yemen-based group whose attempted attacks included the Christmas Day 2009 attempt to blow up a Northwest Airlines flight from Amsterdam to Detroit. 

U.S. security sources said the threat was related to AQAP, but there was not a specific target and it was not limited to U.S. interests but applied more broadly to Western interests. 

A British Foreign Office official said British authorities were in close contact with U.S. authorities. "The British embassies remain open but staff are advised to exercise extra vigilance as we approach Eid," the official said, referring to the Muslim celebration at the end of the month of fasting. 

On Thursday, the State Department said U.S. embassies that would normally be open on Sunday - chiefly those in the Muslim world - would be closed that day because of security concerns, adding that they might be shut for a longer period. 

No information on specific target

The embassies in the following countries will be closed: Afghanistan, Algeria, Bahrain, Bangladesh, Djibouti, Egypt, Iraq, Jordan, Kuwait, Libya, Mauritania, Oman, Qatar, Saudi Arabia, Sudan, the United Arab Emirates and Yemen. 

The consulates in Arbil, Iraq; Dhahran and Jeddah, Saudi Arabia; and Dubai, United Arab Emirates will also be shut. 

The U.S. Embassy in Tel Aviv, which is normally closed to the public on Sunday, said all its facilities would be shut this coming Sunday and workers not essential for the building's security had been told not to come in. 

It also said the American Center in Jerusalem and the Haifa Consular Agency would be closed on Sunday. 

While the U.S. State Department routinely releases what it describes as a "Worldwide Caution" warning U.S. citizens of the general potential danger of attacks around the world, Friday's travel alert was based on more specific information, said one U.S. official who spoke on condition of anonymity. 

The previous "Worldwide Caution" was issued on February 19. 

U.S. officials declined to provide additional details about the intelligence that led them to close the diplomatic missions and to issue the worldwide travel alert.  However, a second U.S. official said there was no information on a specific target, which was the reason for the broad alert. 

The chairman of the U.S. House of Representatives Foreign Affairs Committee, Ed Royce, said on CNN's "New Day" that he and several other lawmakers met two days ago with Vice President Joe Biden to discuss the threat. 

Later on MSNBC, Royce said: "I believe that it is probably now prudent, given the fact that, in this case, we do have this intelligence, to take this step to make certain that we have fully protected our embassy personnel."