MOGADISHU, March 1 (Reuters) - A roadside bomb set by the Somali Islamist group al Shabaab killed at least five soldiers and injured eight others on Tuesday outside the Somali capital Mogadishu, security forces and a spokesman for the militants said.

Al Qaeda-linked al Shabaab frequently targets Somali and African Union security forces in its bid to overthrow the Western-backed Somali government and impose its own version of sharia law in the country.

"A bomb hit a commando convoy," Abdullahi Hussein, a senior police officer in the area told Reuters. He said the attack took place in Alamada village, about 20 km northwest of Mogadishu.

An al Shabaab spokesman confirmed that it had targeted the convoy and claimed a slightly higher death toll.

"We killed six commandoes, injured seven others and the bomb totally destroyed one of their pickups," Sheikh Abdiasis Abu Musab told Reuters. (Editing by Edith Honan Editing by Jeremy Gaunt)