The attack, a "roadside bomb which had been placed in a hole in the ground", according to Nairobi police chief Moses Nyakwama, was detonated during rush hour on Wednesday evening as people returned home from work.

"One person died in hospital and another is still admitted," Nyakwama said, adding that the rest had been released.

Kenya Red Cross said Thursday that the one victim remaining in hospital was in a critical condition.

No one had claimed responsibility immediately for the attack Wednesday, and the Shebab have denied involvement in previous similar attacks.