Kenyan authorities say they suspect Somali al-Shabab militants are behind a grenade attack in the capital, Nairobi that killed at least six people and wounded more than 60.

Internal Security Minister George Saitoti raised the casualty toll on Sunday.

Officials accuse the al-Qaida sympathizers of hurling grenades at the outdoor terminal of a major bus station on Saturday evening.

Deputy Police Spokesman Charles Owino said the grenades were apparently tossed from a vehicle.

“Eyewitnesses 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-Shabab militants.

In recent months al-Qaida formally announced it had formed an alliance with al-Shabab.

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.