A Somali police officer says a suicide car bomber blew himself up near a moving convoy of Somalia's U.S.-trained elite forces in Mogadishu, killing at least four people.

Capt. Mohamed Hussein says the attacker drove his bomb-laden car into a convoy of troops on the airport road in the capital on Sunday. He said most of the casualties were pedestrians walking along the road.

The Alpha Group troops, who are part of Somalia's intelligence forces, often carry out operations against militants in Somalia.

There was no immediate claim of responsibility for the attack. Somali militant group al-Shabab is waging an insurgency against Somalia's government.

The blast comes days after a U.S. airstrike killed al-Shabab's intelligence chief, Abdishakur Tahlil.