A roadside bomb exploded near a crowded passenger bus in the Sri Lankan capital Colombo killing 21 people and wounding 47.
The blast occurred during this morning's rush hour in the southern suburb of Moratuwa.
The military blamed Tamil Tiger rebels for the blast, the latest attack on civilians in or near the capital this year.
It comes as Sri Lanka's military presses its offensive to retake the Tamil Tigers' northern stronghold in daily land, sea and air attacks in a civil war that has killed more than 70,000 people since 1983.
On Wednesday, the military blamed the rebels for a bomb blast on a railway track that wounded 27 civilians in Colombo.
Fighting between the military and Tamil Tigers has intensified since the government formally pulled out of a six-year-old ceasefire pact in January, though a renewed civil war has been raging since 2006.
