A car bomb has exploded at the entrance of Somalia's biggest port in its capital Mogadishu on Sunday, killing at least 16 people, police said.

There was no immediate claim of responsibility though the al Shabaab militant group has been carrying out a series of deadly attacks in Somalia.

Al Shabaab's insurgency aims to drive out African Union peacekeepers, topple Somalia's Western-backed government and impose its strict version of Islam on the Horn of Africa state.