KAMPALA Uganda's President Yoweri Museveni said late on Saturday there had been casualties during an attack by Somalia's Islamist group al Shabaab on a military base manned by Ugandan peacekeepers in the Horn of African country on Friday.

Museveni did not say how many soldiers were killed or wounded but it was the first official admission of losses in the attack among the Ugandan troops who are serving in the African Union Transition Mission in Somalia (ATMIS).

"Condolences to the country and the families of those who died," Museveni said in a statement, adding the country's military had set up a panel to investigate what happened.

Al Shabaab has since 2006 has been fighting to topple Somalia's Western-backed government and establish its own rule based on a strict interpretation of Islamic law.

Museveni said during the attack "some of the soldiers there did not perform as expected and panicked, which disorganized them and the al Shabaab took advantage of that to overrun the base and destroy some of the equipment."

The assailants numbered about 800 and during the attack the Ugandan troops were forced to withdraw to a nearby base, about nine kilometres away, he said.

Al Shabaab fighters targeted the base early on Friday in Bulamarer, 130 km (80 miles) southwest of the capital Mogadishu.

Al Shabaab said in a statement at the time that it had carried out suicide bomb attacks and killed 137 soldiers at the base.

There was no immediate official confirmation of the casualties. Al Shabaab tends to give casualty figures in attacks that differ from those issued by the authorities.

ATMIS has so far not said how many troops were killed or wounded in the attack.

The peacekeeping mission has been in Somalia since 2007 and helps to defend Somalia's central government against the Islamists.

(This story has been refiled to change the day to late Saturday, from Sunday, in paragraph 1)

(Reporting by Elias Biryabarema; editing by Jane Merriman)