A grenade attack in the Kenyan capital of Nairobi has killed at least four people and injured about 40 others.

Officials say the blasts Saturday came from grenades hurled at the outdoor terminal of a major bus station. Deputy Police Spokesman Charles Owino quotes witnesses as saying the grenades were thrown from a moving vehicle.

“Eye witnesses have told us that some people who were in a moving vehicle could have been responsible for throwing hand grenades into crowds that were at the bus station – as they (attackers) moved along the road. So far, we have established three points where the hand grenades could have been thrown, but the teams responsible for the investigations are on the ground, and are yet to give us a full brief on the circumstances.”

This is the latest in a string of grenade attacks in the capital since Kenya sent troops into Somalia in October to fight al Qaida-aligned al-Shabab militants.

Shortly after the attack police arrested a man who claimed to be an al-Shabab member.