A bomb tore through a packed bus carrying civilians Saturday in central Sri Lanka, killing 20 people and wounding 50 others, the military said.

The blast inside the bus occurred at 7:05 a.m. in Dambulla town, about 150 kilometers (90 miles) northeast of the capital, Colombo, said military spokesman Brig. Udaya Nanayakkara, blaming separatist Tamil Tiger rebels.

The bus — traveling to the north-central town of Anuradhapura — was stopped in Dambulla when the explosion hit, Nanayakkara said.

A spokesman for the rebels could not immediately be reached for comment Saturday.

The group, listed as a terrorist organization by the U.S. and European Union, routinely denies responsibility for such attacks.

Violence has intensified on this Indian Ocean island and more than 700 have been killed after the government withdrew from a cease-fire with Tamil rebels last month.

Civilians have bore brunt of the violence since January with three attacks on passenger buses killing dozens, including many schoolchildren.

On Jan. 16 a roadside bomb near the southeastern town of Buttala killed 27 people on a bus. Last Tuesday 18 people were killed in a similar bus attack in the rebel-held north.

Both the government and the rebels blame each other for attacks against civilians.

The Tami Tigers have been fighting since 1983 to create a separate state for ethnic minority Tamils. Fighting has killed more than 70,000 people.