SANAA: Five suspected militants linked to al Qaeda were killed by a U.S. drone attack on Sunday in central Yemen, in what appears to be stepped up strikes by unmanned aircraft on Islamists.

The strike took place in the city of Radaa on a vehicle which was believed to be carrying militants, officials said.

"Five were killed and eight injured and we are still investigating who these men are and in what way they were linked to al Qaeda," one official said.

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.

Washington, which fears the spread of Islamist militancy in Yemen, has stepped up drone attacks this year. At least 14 suspected militants have been killed in air strikes apparently carried out by drones since Friday.

Earlier on Sunday, two al Qaeda-linked militants and a pro-government tribesman were killed in clashes in Yemen's restive south, a local official and a tribesman said.

The Yemeni army helped by local tribes launched a U.S.-backed drive in May to drive Islamist militants from Ansar al-Sharia (Partisans of Islamic Law), an offshoot of al Qaeda, out of several southern towns they had held for more than a year.

The two militants killed in Sunday's violence in Abyan province were from Somalia and Pakistan, the tribesman said.

Ansar al-Sharia has attracted hundreds of foreign fighters since it seized the towns in the south and declared them Islamic emirates. Some of those militants had previously fought in Afghanistan.

A Defence Ministry website said an al Qaeda commander, Khaled Batees, was among eight militants killed by a U.S. drone strike in the eastern province of Hadramout on Friday.

Batees had previously been captured by security forces but escaped prison last year.