There was no immediate claim of responsibility, but the Islamist militant group al Shabaab has frequently set off bombs or launched gun attacks in Mogadishu. It promised more attacks after it lost control of a major coastal stronghold a week ago.

"Now I see six dead bodies," police officer Major Nuur Farah told Reuters, adding that other casualties had been taken to hospital after the explosion. "We believe al Shabaab is behind the blast."

Reuters witnesses at the scene, which lies along a major Mogadishu thoroughfare, saw at least three dead bodies. The gate and chairs of the Oromo cafe were destroyed, and blood was spattered at the scene.

The wail of ambulance sirens filled the air after the explosion at a busy time of the evening in the city, which the government is struggling to secure even though al Shabaab militants lost control of the capital in 2011.

Al Shabaab wants to topple the government, which it says is a puppet of Western powers, and aims to drive out African Union peacekeepers, who still provide the backbone of security as the Somali army is slowly rebuilt to form a national force.