Up to 18 Yemeni soldiers and security guards have been killed in a car bombing and grenade attack on the intelligence service headquarters in Aden.

The ministry has said that more bodies were believed buried under the rubble of the building, part of which was levelled in the attack in Aden, a southern port city.

At least seven others were injured before the militants fled.

Witnesses said militants had fired rocket-propelled grenades at the intelligence service's three-storey building, shattering windows and setting it on fire.

The militants had stopped their vehicle in front of an adjacent five-storey television building, blown up a military vehicle guarding the compound.

They then attacked the intelligence service building with automatic fire and rocket propelled grenades before fleeing.

The United States has been pouring aid into Yemen to stem the threat of attacks from al-Qaeda in the Arabian Peninsula.

It is attempting to try to prevent any spillover of violence into neighbouring Saudi Arabia, the world's top oil exporter.

Last year, a US-backed offensive drove al-Qaeda offshoot Ansar al-Sharia (Partisans of Islamic Law) from cities they had seized in an uprising against former president Ali Abdullah Saleh.

But militants have carried out deadly suicide bombings on high-profile military and security targets since June, exposing the government's vulnerability.