Suspected al Qaeda militants killed five Yemeni soldiers in their sleep early on Sunday in an attack on forces guarding the country's only liquefied natural gas (LNG) export terminal, a local official said.

The attack follows an escalating campaign of drone strikes by the United States over the past two weeks after a worldwide travel warning that forced Washington to close its embassy in Sanaa and evacuate some staff.

The official said the gunmen infiltrated a checkpoint guarding the Balhaf LNG terminal in the southern Shabwa province, killed a guard and then entered a cargo container where the soldiers were sleeping and killed them.

The attackers fled in a vehicle, he said.

A Yemeni government spokesman said last week that the $4.5 billion gas facility, jointly managed by Yemen LNG and France's Total, was one of two energy targets that suspected al Qaeda militants had been plotting to attack.

The United States and other Western countries last week closed down some of their diplomatic missions in the Middle East, including in Yemen, following warnings of a threat.

Washington responded by stepped up drone strikes on suspected al Qaeda targets in Yemen which killed at least 15 people in three days.

The Balhaf facility, the largest industrial project ever undertaken in Yemen, opened in 2009. It is heavily guarded by Yemeni troops.

It supplies gas cooled to liquid for export by ship, under long-term contracts to GDF Suez, Total and Korea Gas Corp. – Reuters