A bomb and shooting attack blamed on Tamil separatists ripped through a packed civilian bus Wednesday, killing 25 people in southeastern Sri Lanka as the government officially withdrew from a tattered cease-fire with the rebels.

Military spokesman Brig. Udaya Nanayakkara said it was clear the rebels — accused of killing two more people as they retreated into the bush — were behind the assault, the latest in a string of recent attacks in government-held territory.

"There are no other groups operating in the area," he said.

Spokesmen for the rebels could not immediately be reached for comment. However, the group, listed as a terror organization by the U.S. and European Union, routinely denies responsibility for such attacks.

Such an attack by the group would highlight its increasing determination to hit targets in the generally peaceful south as the military presses ahead with an offensive against rebel-held territory in the north.

President Mahinda Rajapaksa condemned the attack.

"This is a brazen demonstration to the whole world of its unchanged commitment to terrorism and the absolute rejection of democracy and all norms of civilized behavior," he said.

The attack occurred early Wednesday in the remote town of Buttala, about 150 miles southeast of Colombo. A bomb exploded near a bus, shattering its windows and causing panicked passengers to flee. When they did, gunmen opened fire, witnesses said.

"Everyone that got out through the doors, they shot and killed," said a 25-year-old passenger who gave his name as Sampath. "I jumped from the window and just escaped."

Officials said the blast came from a 44-pound mine just yards from the road.

The attack killed 25 people and injured 63 others, Nanayakkara said. Earlier, he had said 26 people were killed. He gave no explanation for the discrepancy.

The assailants retreated into the bush, shooting and hacking farmers they met along the way, killing two more people and injuring three, he said.

Doctors from Colombo were flown to the area by emergency helicopters to treat the wounded and medical workers said many of those killed were hit by gunfire. The Sri Lankan health services made an emergency appeal for people with rare blood types to donate blood.

Soon after the attack, a second roadside bomb struck an armored military vehicle in the same region, lightly injuring three soldiers, Nanayakkara said. In response, local authorities closed schools for three days.

Hours later, government forces in the eastern city of Trincomalee killed a local rebel leader, the military said.

The bombings came on the final day of the 2002 cease-fire agreement, which had largely broken down over the past two years amid renewed fighting.

Though scrapping the truce has little direct impact on the raging war, the Cabinet's unanimous decision to end the deal was criticized by peace mediators and foreign governments, who worried it would make it even more difficult to end the decades-old conflict.

In the two weeks since the government announced it would annul the cease-fire Wednesday, more than 300 people have been killed in violence along the front lines in the north, according to military figures.

In the latest violence, 13 insurgents and two soldiers were killed in the fighting Tuesday, the military said.

Each side often gives different accounts of the fighting, exaggerating enemy casualties while underreporting its own. Independent confirmation is unavailable since the battle zone is restricted.

The most immediate effect of the end of the cease-fire was the dissolution of the Sri Lanka Monitoring Mission, one of the few independent groups with access to both rebel-held territory and the government.

At a final news conference, the head of the monitoring mission, Lars Johan Solvberg, said the number of cease-fire violations had grown so large by last year the mission was no longer able to track them.

He worried the situation could worsen once his team leaves. "Our presence in the north and east at the local level has had an impact," he said.

The Tamil Tigers have been fighting since 1983 for an independent state for Sri Lanka's ethnic Tamil minority in the north and east after decades of being marginalized by Sinhalese-dominated governments. The fighting has killed more than 70,000 people.

President Mahinda Rajapaksa has said he abandoned the cease-fire because it wasn't working and the rebels used it as cover to build up their military strength. At least 5,000 people have been killed since the cease-fire was signed.