Security is especially tight in Yemen\'s capital Sanaa Intercepts between al-Qaeda chief Ayman Al-Zawahiri and the leader of the group\'s Yemen affiliate sparked Washington\'s closure of US missions overseas and global travel alert, US media reports. The New York Times said in its online edition that the electronic communications last week revealed that Zawahiri had ordered Nasser al-Wuhayshi, the head of al-Qaeda in the Arabian Peninsula, to carry out an attack as early as this past Sunday.
CNN, meanwhile, reported that Zawahiri told Wuhayshi to \"do something,\" causing officials in both Washington and Yemen to fear an attack was imminent.
As a result, roughly two dozen US diplomatic posts were shut across the Middle East Sunday.
The US State Department, acting \"out of an abundance of caution\" has extended some of the closures, saying 19 diplomatic outposts would remain shut through Saturday.
A US official told the Associated Press news agency that Zawahiri\'s message had been picked up several weeks ago and appeared initially targeted at Yemen.
US lawmakers have said it was a huge plot in the final stages, but have offered no specific details.
\"Our current information suggests that al-Qaeda and affiliated organisations continue to plan terrorist attacks both in the region and beyond. And our information suggests that they may focus efforts to conduct attacks in the period between now and the end of August,\" White House spokesman Jay Carney said
Al-Qaeda in the Arabian Peninsula is seen by Washington as the most active branch of the jihadist network.
Several US allies, including Britain, France, Germany and Norway have also announced closures of some of their missions in the region.
The US closure list includes 15 embassies or consulates that were shut on Sunday -- the fifteenth anniversary of al-Qaeda\'s attacks on US embassies in East Africa -- as well as four additional posts.
Lawmakers in Washington described the threat level as very serious.
Michael McCaul, chairman of the House Homeland Security Committee dubbed the intelligence \"probably one of the most specific and credible threats I\'ve seen, perhaps, since 9/11.\"
Saxby Chambliss, vice chairman of the Senate Intelligence Committee, said that the level of chatter among alleged terrorists was \"very reminiscent of what we saw pre-9/11\".
General Martin Dempsey, chairman of the US Joint Chiefs of Staff, told ABC News the threats were \"more specific\" than previous threats, although the exact target was unknown.
ABC News cited an unnamed US official as saying there was concern al-Qaeda might deploy suicide attackers with surgically implanted bombs to evade security.
The posts to be closed include Abu Dhabi, Amman, Cairo, Riyadh, Dhahran, Jeddah, Doha, Dubai, Kuwait, Manama, Muscat, Sanaa, Tripoli, Antananarivo, Bujumbura, Djibouti, Khartoum, Kigali and Port Louis.
New closures were announced in Madagascar, Burundi, Rwanda and Mauritius. The outposts that are reopening include those in Afghanistan, Algeria, Bangladesh, Mauritania, Iraq and Israel.
Security was especially tight in Yemen\'s capital Sanaa.
Several European countries have temporarily shut missions in Yemen and the UK Foreign Office is advising against all travel to the country.
Soldiers with armored personnel carriers were stationed outside the buildings as police and army checkpoints went up on all the city\'s main thoroughfares.
Residents said they heard the sound of a drone overhead, which could only be American as Washington is the sole power to operate the unmanned aircraft in the region.
\"I\'ve spent 21 years in the CIA, and I don\'t think I\'ve ever seen 22 embassies closed simultaneously. This is very, very unusual,\" Robert Baer, a former CIA officer in the Middle East, told CNN.
Baer said the US action comes amid an al-Qaeda resurgence, including recent prison breaks in Libya and Iraq and turmoil in Egypt, Mali and elsewhere in the region.
On Saturday, the global police agency Interpol stoked terror fears further by issuing a security alert over hundreds of militants freed in jail breaks.
Interpol said it suspected al-Qaeda was involved in the mass breakouts in nine countries, notably Iraq, Libya and Pakistan.