The U.S. military evacuated non-essential U.S. government personnel from Yemen on Tuesday due to the high threat of attack by al-Qaeda that has caused temporary shutdowns of 19 American diplomatic posts across the Middle East and Africa.

The State Department said it had ordered the evacuation "due to the continued potential for terrorist attacks" and said U.S. citizens in Yemen should leave immediately because of an "extremely high" security threat level.

"As staff levels at the Embassy are restricted, our ability to assist U.S. citizens in an emergency and provide routine consular services remains limited," the travel warning said.

Defence Department Press Secretary George Little said the U.S. Air Force transported State Department personnel out of Sanaa early Tuesday. "The U.S. Department of Defence continues to have personnel on the ground in Yemen to support the U.S. State Department and monitor the security situation," Little said.

The Canadian government's advice for travellers had already been to avoid Yemen.

"You are strongly urged to leave the country immediately if it is safe to do so," the Foreign Affairs advisory says, and warns that Canada's ability to provide assistance is "extremely limited."

A statement by the Yemeni Embassy in Washington says Tuesday's decision to evacuate diplomatic staff "serves the interests of the extremists and undermines the exceptional cooperation" between Yemen and the international community in the fight against terrorism.

A U.S. intelligence official and a Mideast diplomat told The Associated Press that the current shutdown of embassies in the Middle East and Africa was caused by an intercepted secret message between al-Qaeda chief Ayman al-Zawahri and Nasser al-Wahishi, the leader of the Yemen-based al-Qaeda in the Arabian Peninsula, about plans for a major attack. The officials spoke on condition of anonymity because they were not authorized to discuss the matter publicly.

AQAP has been widely considered al-Qaeda's most dangerous affiliate.

U.S. again training Yemeni military

The U.S. has hit extremist leaders in Yemen with drone strikes. On Tuesday, Yemeni security officials said a suspected U.S. drone killed four alleged al-Qaeda members in a volatile eastern province. The drone fired a missile at a car carrying the four men, setting it on fire and killing all of them, the officials said.

The Yemeni officials, speaking on condition of anonymity because they are not allowed to talk to the media, said they believe one of the dead is Saleh Jouti, a senior al-Qaeda member. It's the fourth drone attack in the past week to hit a car believed to be carrying al-Qaeda members.

The State Department on Sunday closed a total of 19 diplomatic posts until next Saturday. They include posts in Bangladesh and across North Africa and the Middle East as well as East Africa, including Madagascar, Burundi, Rwanda and Mauritius.


View U.S. embassies closed as of August 4 in a larger map

Britain's Foreign Office also announced that it had evacuated all staff from its embassy in Yemen due to security concerns. The office said the British Embassy staff were "temporarily withdrawn to the U.K." on Tuesday, but declined further comment. Previously, the U.K. had said the embassy would be closed until the end of the Muslim festival of Eid later this week.

AQAP, gathered in small cells scattered across Yemen's vast under-governed regions, has proven to be a tenacious enemy.

Officials say al-Zawahri, who took over for Osama bin Laden and works from Pakistan, has reached out to the Yemeni branch, further signalling the AQAP is once again looking to target U.S. and Western interests after a sustained period of more local and regional focus.

The latest warnings raise questions about how successful America's war on terror has been and whether al-Qaeda has been able to reorganize and reconstitute itself since Osama bin Laden's death in May 2011 in Pakistan.

And, although U.S. officials agreed a year ago to restart once-frozen military aid to Yemen, it's unclear how much of the new aircraft and weapons have arrived. The U.S. military is once again training Yemeni special operations forces and has delivered more than a dozen helicopters to the Yemeni military, U.S. defence officials said.

Unstable government, overstretched military

The embassy closures came one day after a meeting between President Barack Obama and Yemeni President Abdo Rabu Mansour Hadi.

Even though AQAP lost U.S. citizen Anwar al-Awlaki — one of its key inspirational leaders — to a U.S. drone strike in 2011, al-Wahishi and the group's master bomb maker, Ibrahim Hassan al-Asiri, remain on the loose and determined to target the U.S. and other Western interests.

The group is linked to the attempted Christmas Day 2009 bombing of an airliner bound for Detroit and explosives-laden parcels intercepted aboard cargo flights a year later — both incidents involving al-Asiri's expertise.

In recent years, however, AQAP has been focused more on making gains at home, taking advantage of an unstable government and overstretched military.

With files from The Canadian Press