COLOMBO, Sri Lanka — A bomb on a Sri Lankan passenger bus killed at least 15 people and wounded dozens more Saturday, officials said, blaming Tamil Tiger rebels for the country’s second bus bombing in as many days.The blast, which police suspect was triggered by a female suicide bomber, appeared to signal an escalation of the bloody ethnic conflict ravaging the island nation off southern India.

Police blamed Tamil Tiger rebels for the bus attack in the coastal town of Meetiyagoda, 60 miles south of the capital, Colombo, and near a number of popular resort towns.

Though violence has risen sharply in Sri Lanka over the past year, most of it has occurred in the ethnic Tamil-dominated north and east, where the rebels run their own de facto state.

Officials said the bus wreckage indicated that a suicide bomber may have been behind the attack, which ripped through the bus on the crowded southern coast road early Saturday afternoon.

“There is a female body inside the bus, and looking at the damage the blast has caused around her, we suspect that she could have been a suicide bomber,” said senior police official Upul Ariyaratne.

About 65 passengers had been on bus, Ariyaratne said, and some 40 had been admitted to hospitals.

The Tigers have made suicide bombings a hallmark of their two-decade campaign to carve out a separate state for the minority Tamils, who suffered years of discrimination by the Sinhalese-dominated government.

However, the Tigers denied any role in Saturday’s bloodshed.

“We totally deny that (the bus bombing). We did not do that,” the rebels’ military spokesman, Rasiah Ilanthirayan, told The Associated Press by telephone from the group’s northern stronghold, Kilinochchi.

Sri Lankan officials said the two bombings — six people were killed in a similar bus attack Friday on a highway northeast of Colombo — indicate that a stepped-up government military campaign has weakened the rebels, officially called the Liberation Tigers of Tamil Eelam or LTTE.

“The LTTE is losing their strength in the east. Because of this, they are targeting innocent civilians,” said military spokesman Brig. Prasad Samarasinghe.

Both bus explosions came days after the rebels warned the government of “serious repercussions” for government airstrikes they said had killed 16 Tamil civilians, including eight children, in a Tiger-controlled northwestern area. The military said it targeted only rebel positions in the airstrikes Tuesday.

“This looks like a retaliatory attack for the air force raids,” said Sunanda Deshapriya, an independent political analyst.

“The LTTE has gone back to its previous tactic of attacking Sinhalese civilians,” Deshapriya said. “It wants to send a message through terror again.”

In other violence Saturday, three separate roadside bombings, blamed on the insurgents, killed four soldiers and a civilian in the north.

A 2002 cease-fire between the rebels and the government has come under serious threat as more than 3,600 fighters and civilians were killed in renewed fighting in 2006. The cease-fire still officially holds.

The civil war has claimed about 68,000 lives, and displaced 1.6 million people.