A wounded man is brought into the hospital on March 10 after a bomb at a bus station in Nairobi that left at least 6 dead.

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NEW: At least 68 others are injured

NEW: Police suspect Al-Shabaab or sympathizers of Al-Shabaab

Grenade attacks have rocked Nairobi in recent months

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 cannot 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.