SANAA - The United States and Britain told their citizens in Yemen on Tuesday to leave the country immediately.
The State Department also said it had ordered non-essential US government staff in Yemen to leave the country, due to the threat of "terrorist attacks", the US State Department said in a statement.
"The Department urges US citizens to defer travel to Yemen and those US citizens currently living in Yemen to depart immediately," the statement posted on its website said.
"On August 6, 2013, the Department of State ordered the departure of non-emergency US government personnel from Yemen due to the continued potential for terrorist attacks," it added.
"In response to a request from the US State Department, early this morning the US Air Force transported personnel out of Sanaa, Yemen, as part of a reduction in emergency personnel," Pentagon spokesman George Little said in a statement.
Meanwhile, the UK urged all British nationals to leave Yemen immediately, the Foreign Office said on its website.
"If you don’t leave the country now while commercial carriers are still flying it is extremely unlikely that the British government will be able to evacuate you or provide consular assistance," it said.
Britain said it had withdrawn all staff from its embassy in Sanaa, and extended the closure of the mission until further notice.
"Due to increased security concerns, all staff in the British Embassy have been temporarily withdrawn and the Embassy will remain closed until staff are able to return," the Foreign Office said on its website.
"There is a very high threat of kidnap from armed tribes, criminals and terrorists. Be particularly vigilant during Ramadan, when tensions could be heightened," it said.
The new measures came after at least four suspected al-Qaida members were killed in what local tribal leaders said was a US drone strike in central Yemen early on Tuesday.
Drone strikes on suspected al-Qaida targets in Yemen are usually carried out by US forces, although Washington does not comment publicly on the practice.
Washington on Friday issued a heightened security warning that prompted the closure of several Western embassies in Yemen and several US missions across the Middle East and Africa.
The New York Times reported on Monday that the closure of the US embassies was prompted by intercepted communication between al-Qaida leader Ayman al-Zawahri and Nasser al-Wuhaishi, head of Yemen-based al-Qaida in the Arabian Peninsula (AQAP).
Security in Yemen is a global concern as it is home to AQAP, considered one of the most aggressive branches of the global militant organization, and shares a long border with Saudi Arabia, a US ally and the world's top oil exporter.
The US government backs Yemeni forces with funds and logistical support.
Yemeni authorities issued a statement early on Tuesday listing 25 "most wanted terrorists" it said were planning to carry out attacks in the country during the Muslim Eid al-Fitr holiday this week.
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