NAIROBI - Twenty eight people were injured in the Kenyan capital on Sunday in a blast that police suspect went off at a hardware shop, setting a petrol station on fire.The people were being treated at a local hospital for injuries from the blast, a Reuters photographer said. The cause of the blast was not immediately clear."We suspect an explosion inside a hardware shop adjacent to a petrol station, setting the pumps on fire. The fire has now been brought under control," Charles Owino, deputy police spokesman told Reuters by telephone.Television footage showed widespread destruction at the scene with crowds rummaging through debris. Owino said they were still compiling details of injuries.The east African nation has suffered bombings in the past, the most recent being a bomb on a Kampala-bound bus, that killed two people in December.