Colombo, June 6 : At least 20 people have been killed and 40 injured in a bomb explosion in a bus in Colombo.

The explosion in a southern suburb of Colombo came two days after suspected Tamil Tiger rebels blew up a rail track near the Sri Lankan capital wounding 27 people.

BBC quoted military spokesman Brig Udaya Nananyakkara as saying, the Tamil Tiger rebels had detonated a roadside bomb that targeted the bus in the suburb of Moratuwa.

The explosion comes as the Sri Lankan army continues a large-scale offensive against Tamil Tiger separatists in the north of the country.

On Wednesday, at least 24 people were injured when a packed commuter train in the city was hit by a bomb. (ANI)