Nairobi , Kenya ( CNN ) -- The death toll has risen to six following an attack on a Kenyan bus station that left dozens wounded , the Red Cross said Sunday . At least 68 people are undergoing treatment at a Nairobi hospital , according to the agency . The explosions , which authorities believe are grenade attacks , occurred Saturday at a normally-crowded bus station in central Nairobi . `` We still need to complete investigations and we can not immediately confirm who did this , but we highly suspect that it is Al-Shabaab or sympathizers of Al-Shabaab , '' said Charles Owino , the police deputy spokesman . `` Eyewitnesses say that grenades were thrown from a vehicle and the suspected perpetrators fled from the scene . '' There have been several instances of grenade attacks at bus stations and at a bar in Nairobi in recent months . One person was killed and 20 injured in October when an attacker hurled grenades into a bar and a bus station . In that attack , a Kenyan man pleaded guilty to being a member of the Islamic militant group Al-Shabaab and was charged with causing grievous bodily harm . The East African nation has been on edge since it sent its troops into Somalia to pursue Al-Shabaab militants after the abductions of tourists and aid workers in Kenya . It blames the abductions on Al-Shabaab , which has denied involvement . Al-Shabaab , which the U.S. considers a terror group , has threatened to attack Kenya if it does not withdraw its forces from Somalia .
NEW : At least 68 others are injured . The blast is the deadliest attack in Kabul since a suicide car bombing killed at least 80 people on April 7, 2009. Police suspect Al-Shabaab or sympathizers of Al-Shabaab . Grenade attacks have rocked Nairobi in recent months .