ADEN/SANAA: Eight Islamist militants were killed by a U.S. drone strike on Friday in a remote part of Hadramout, a Yemeni official said, the third such strike in the eastern Yemeni province this week.

Yemen's defence ministry said on its website that eight al Qaeda members were killed in an air strike on their vehicle in the isolated, desert district of Hawra. The local official, who declined to be named, said it was a drone strike.

The men were heavily armed, carrying machine-guns and explosives, the ministry said. The local official said the men were thought to have been on the way to carry out an attack.

It was not possible to verify the details independently given the remoteness of the region.

Washington, which fears the spread of militants in Yemen, has stepped up attacks by unmanned aircraft this year.

Al Qaeda in the Arabian Peninsula is based in Yemen and has mounted operations in neighbouring Saudi Arabia as well as attempting to launch attacks against the United States.

At least six suspected Islamist militants have been killed in air strikes apparently carried out by drones since Tuesday.

In a statement issued on Friday, a group of clerics and preachers from southern Yemen said one of their members had been killed in one of the recent U.S. drone attacks.

"Among the four killed in an attack launched by a U.S. aircraft in the al-Qatn district of Hadramout on Wednesday was one of our members, Salem bin Ahmed bin Ali Jaber, who had no link to al Qaeda," the Union of Clerics and Preachers of Yemen's Southern Provinces said in a statement.

"He was known for his moderate ... approach that was far from being excessively strict."

The impoverished Arabian Peninsula state has been in turmoil since an uprising last year which eventually forced veteran ruler Ali Abdullah Saleh to step down in February.

Islamist militants gained ground during the unrest, taking control of several towns in south Yemen.

The army, with backing from the United States, has forced them out of some areas this year but they have hit back with a series of suicide bombings targeting government institutions.

On Thursday, a Yemeni intelligence officer was killed on the street in the capital Sanaa by a gunman shooting from a motorbike. It was not immediately clear who was behind the attack.