Kenyan officials say al-Shabab militants are responsible for a grenade attack in the capital of Nairobi that killed at least four people and injured about 40 others.

Officials accuse the Al-Qaida sympathizers of hurling grenades at the outdoor terminal of a major bus station Saturday. 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 gun, bomb and grenade attacks that have killed dozens of people since Kenya sent troops into Somalia in October to fight al Qaida-aligned al-Shabab militants.

Authorities say a Kenyan supporter of al-Shabab militants was arrested and convicted following some of the earlier incidents, but no one has claimed responsibility for Saturday's killings.