In depth

 Somalia's crossroads
 Profile: Sharif Ahmed
Timeline: Somalia
Restoring Somalia
A long road to stability
Al-Shabab: Somali fighters undeterred
 Somaliland: Africa's isolated state

Several residents said that two civilians had been hit by stray bullets near the scene of clashes and three others were killed when a mortar shell struck a house.

A medical official said that more than 20 wounded people had been transferred to the city's Medina hospital.

The clashes follow Sunday's suicide bomb attack on an AU base in the Somali capital, which left 11 Burundi soldiers dead.

The bombing, for which the al-Shabab armed group claimed responsibility, was the deadliest so far against the African Union Mission in Somalia.