Fighters from Somalia's Shebab Islamist group attacked a government military base in Mogadishu on Saturday, where a blast was followed by an exchange of gunfire, officials and witnesses said.

Enemy "elements attacked a Somali military base near the industrial road (north of the city centre), but they were defeated and suffered losses", Colonel Abdallah Mohamed of the Western-backed government forces told AFP.

"Mujahideen fighters hit the Xero-Jamal site where the enemy is positioned", said Shebab commander Sheikh Ibrahim Abu Yahya, who also claimed dozens of pro-government fighters were killed.

"There was a very strong explosion, like in a suicide attack, before an exchange of gunfire," a witness, Abdikarim Dinow, said.

Pro-government forces sent ambulances to the scene of the clashes, according to another witness, Ahmed Moalim.

Neither side provided an explanation as to the nature of the explosion described by witnesses.

The Shebab, who control large swathes of territory in south and central Somalia, withdrew from their positions in Mogashishu in early August following a government offensive launched in February.

They have claimed credit for a series of bombings since, including an October 4 blast at a government complex that killed 82, the deadliest single attack ever committed in Mogadishu.