George Saitoti said Sunday that 63 people were injured in the attack at a downtown bus stop in Nairobi on Saturday night. Police said it seemed that three explosive devices, possibly grenades, had been thrown from a moving vehicle into a crowd.

Saitoti says Kenyan authorities suspect sympathizers with Somalia’s Al-Qaeda-linked Al-Shabab militia are behind the attack.

The group has been linked to a string of attacks on Kenyan soil after Kenya sent troops into Somalia in October.

Kenya was worried that instability from Somalia’s 21-year-old civil war was spilling across the two countries’ shared border.