Four alleged al-Qaida members were killed in Yemen by a suspected U.S. drone attack on Tuesday. Intelligence that suggested a possible attack by al-Qaida had prompted a shutdown of 19 U.S. diplomatic offices throughout the Middle East and North Africa over the weekend and now staff from the U.S. and British embassies in Yemen have evacuated, according to the Associated Press.

In addition to clearing out the embassies all U.S. citizens were urged to leave Yemen after it was learned that the head of al-Qaida, Ayman al-Zawahiri, had called for an attack to be carried out from its Yemeni branch, according to the Washington Post.

Drone strikes on Yemen are run from a military base located in neighboring Djibouti just across the Red Sea. Tuesday's strike marked the fourth in the last two weeks, far more than usual.

Officials from Yemen say that an American drone shot a missile at a car with four male passengers killing them all. The strike took place in the al-Arqeen district of Marib province east of the capital of Sanaa. It is believed that a senior al-Qaida member, Saleh Jouti, was killed in the strike, according to the Associated Press.

The names of 25 wanted al-Qaida members who were suspected to be planning attacks within the capital of Sanaa were released by the Yemeni government on Monday. It was believed that the attacks would focus on both Yemeni government offices and foreign installations, according to the Associated Press.

An intercepted call between al-Zawahiri and Nasser al-Wuhayshi, the head of Yemen's branch of al-Qaida, prompted the closure of the embassies in part because it is extremely rare that two of the highest ranking al-Qaida members talk to each other. In the intercept Sunday was mentioned as the day the attacks were supposed to take place, according to the New York Times.

"This was significant because it was the big guys talking, and talking about very specific timing for an attack or attacks," an American official told the New York Times.

The branch of al-Qaida based in Yemen calls itself al-Qaida Arabian Peninsula and has been under immense pressure from American drone strikes as well as the Yemeni Army over the last year and a half. The group has lost much of the territory it once held and has had to go back into hiding but still remains quite powerful, according to the New York Times.

"The question I have is, if the Obama administration is confident that its strategy in Yemen is correct, then why is al-Qaida growing in Yemen and why is the group still capable of forcing the United States to shut down embassies in more than a dozen countries?" Gregory Johnsen, a Yemen expert at Princeton, told the New York Times.

Al-Qaida Arabian Peninsula is thought to be the most effective and dangerous branch of the terrorist organization. Al-Wuhaysi has recently been promoted to the second in command of all of al-Qaida, a troubling development to terrorism experts, according to the Washington Post.

"It's very worrisome because al-Qaida in the Arabian Peninsula is the most effective and threatening affiliate," Bruce Hoffman, a terrorism expert and professor at Georgetown University, told the Washington Post. "So now the leader of the most consequential affiliate has an intimate command role in the overall organization. From Zawahiri's point of view, there's no better exemplar of the al-Qaida brand than AQAP."

The closed embassies and consulates are expected to remain closed until at least this Saturday.