A second explosion has occurred in the Kenyan capital Nairobi, killing at least one person.
The blast took place near a bus stop where working class Kenyans gather to find transportation home.
The Kenyan Red Cross reported on its Twitter feed that one person was killed and eight others were taken to hospital.
It came after an earlier grenade blast in a pub in the city left 13 people injured.
The blasts came two days after the US had warned of possible terror attacks in Kenya.
Police commissioner Mathew Iteere told a news conference earlier that the authorities could not yet name suspects from the first blast.
"It is too early at this point in time to give a conclusive answer," he said.
Al-Shabab is loosely affiliated with al Qaida and counts militant veterans of the Afghanistan and Iraq wars among its ranks. The militant group carried out twin attacks in Kampala, Uganda, in July 2010 that killed 76 people.