WASHINGTON - The State Department issued a worldwide travel alert yesterday, warning citizens of potential terror attacks in the Middle East and northern Africa by al-Qaida and its affiliates.

WASHINGTON — The State Department issued a worldwide travel alert yesterday, warning citizens of potential terror attacks in the Middle East and northern Africa by al-Qaida and its affiliates.

“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,” the department said. The attacks are seen as occurring in or emanating from the Arabian peninsula, according to the statement, and “may involve public transportation systems and other tourist infrastructure.”

The department also listed 21 U.S. embassies and consulates that will be closed this weekend as a precaution. Those being shut are in the Mideast, northern Africa and southern Asia, including in Libya, Egypt, Yemen and Afghanistan, according to a list posted on the department’s website.

“The Department of State has instructed certain U.S. embassies and consulates to remain closed or to suspend operations on Sunday,” department spokeswoman Marie Harf said Thursday.

The British Foreign Office said yesterday on its Twitter feed that its embassy in Yemen will be closed Sunday and Monday, with some of the staff being temporarily withdrawn. It said embassies in Saudi Arabia, Qatar, Kuwait, the United Arab Emirates, Iraq and Bahrain will be open on Sunday, though staff members are advised to be extra-vigilant.

Delta Air Lines, US Airways and American Airlines are monitoring the travel situation and haven’t issued waivers letting passengers rebook flights without paying fees, spokesmen said. United Airlines declined to comment.The alert has not changed procedures at Port Columbus or Rickenbacker airports.“We’re aware of the alert and ever-vigilant, but we don’t have any specific new directives or procedures in place that were sent down from the federal level to us,” said David Whitaker, the Columbus Regional Airport Authority’s vice president of business development.The top Democrat on the House Intelligence Committee, Rep. C.A. “Dutch” Ruppersberger of Maryland, said information coming in to security officials warranted a broad warning to citizens.

“We got intelligence, and not just the normal chitchat, that there could be an attack on Americans or our allies,” Ruppersberger told reporters at the U.S. Capitol. “Putting it out there, that also gives notice to the people that are planning it: We know something’s out there.”

There’s always a chance that the information on the planned attacks is intentionally misleading in an attempt to divert attention and security from the location, timing or nature of an actual plot, said an official of a U.S. agency who called the intelligence credible but not ironclad and spoke on condition of anonymity because of the sensitivity of the matter.

The State Department pledged to increase security at embassies and consulates after the attack on a U.S. mission in Benghazi, Libya, on Sept. 11, 2012, led to the death of U.S. Ambassador Chris Stevens and three other Americans. The CIA said it repeatedly had warned the State Department of terrorist threats in Benghazi before the attack, according to emails released later by the White House.

The State Department had issued a similar warning of possible attacks before that.

Rep. Ed Royce of California, the Republican chairman of the House Foreign Affairs Committee, said yesterday on CNN that it’s his understanding that the latest threat “emanates in the Middle East and in Central Asia.”

The British Foreign Office said it will review safety at its embassies after the U.S. announcement, according to The Telegraph newspaper. Dispatch Reporter Steve Wartenberg contributed to this story.