A bomb and shooting attack blamed on Tamil separatists ripped through a packed civilian bus Wednesday, killing 26 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 were behind the assault, the latest in a string of attacks in government-held territory in recent months. "There are no other groups operating in the area," he said. Spokesmen for the rebels could not immediately be reached for comment. But the group, listed as a terror organization by the U.S. and European Union, routinely denies responsibility for such attacks. If the Tamil Tigers are responsible, it highlights their 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. The bomb struck the bus in the remote town of Buttala, about 150 miles southeast of Colombo, about 7:30 a.m., Nanayakkara said. Moments later, a barrage of gunfire hit the vehicle, he said. The attack killed 26 people and injured 64 others, he said. Doctors from Colombo were being flown to the area by emergency helicopters to treat the wounded and medical workers said many of those killed were hit by gunfire. 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 to the attacks, local authorities announced the closure of all schools in the province for three days. The bombings came just hours after the official end 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 as a move that 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 Tuesday in fighting along the front lines in the north, the military said Wednesday. 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. The Nordic group had been set up to monitor the truce, but increasingly found itself issuing weekly reports on the state of the fighting. 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. The cease-fire was hailed as a crucial step toward ending the fighting when it was initiated in 2002, and for several years the violence plummeted. But new fighting broke out two years ago, leading to a wide-scale government offensive that forced the rebels out of the cities and towns of the east in July. The military then turned its attention to the rebel's heartland in the north, and senior officials said they hope to crush the Tigers by the end of the year, an operation that might be easier with the Nordic monitors gone. Japanese peace envoy Yasushi Akashi, who rushed to Sri Lanka for talks before the cease-fire expired, said Tuesday his country was concerned that the end of the truce "may prompt the pursuit of military solution of the conflict, with dire humanitarian consequences."