Ethiopian Prime Minster Meles Zenawi said Friday he would pull troops out of Somalia "as soon as feasible," admitting for the first time that forces had crossed into the war-torn neighbouring country.

"The decision has all along been to help the TFG and we will withdraw our troops as soon as feasible," Meles told reporters in the Ethiopian capital, referring to Somalia's transitional government.

"We are not going to create a vacuum, we expect the AMISOM troops to be able to fill in the gaps before we withdraw," he added.

Columns of Ethiopian soldiers rolled into Somalia in November to fight al-Qaeda linked Islamist rebels, but Addis Ababa had previously denied their presence.

The African Union Mission in Somalia (AMISOM) has some 10,000 troops in the Somali capital Mogadishu to protect the fragile Western-backed Somali government.

On Tuesday, a Shebab suicide bomber blew himself at an Ethiopian army base in the central Somali town of Beledweyne.

Ethiopia first deployed troops in Somalia in 2006 to oust an Islamist movement that ruled much of southern Somalia, but withdrew three years later after failing to stamp out the group.

Armies from neighbouring countries are converging on the Shebab. Kenya sent in troops and tanks into southern Somalia in October to fight the rebels it accuses of carrying out cross-border raids and kidnappings.

The attack in Beledweyne was the latest in a string of blasts including roadside bombs and grenade explosions set off in recent months in the war-torn Horn of Africa nation.