Government soldiers backed by artillery and airpower seized a key rebel enclave in the east Monday, the military said, claiming the first significant territorial change since a cease-fire in the island nation's civil war four years ago.

But the commander of the ethnic Tamil rebels in the east, S. Elilan, said the battle for the town of Sampur was still raging. "We are fighting them. This is our territory, we can't let it be invaded by the enemy," he said.

Recent weeks of near-daily airstrikes and artillery duels between Tamil rebels and government troops shattered the truce on the island just off India's southern tip, and the military offensive at Sampur was a further escalation in a situation verging on all-out war.

Soldiers entered Sampur on Monday and were clearing the area of land mines and explosives left by retreating rebels, said a military spokesman, Brig. Prasad Samarasinghe.

CountryWatch: Sri Lanka

"We are now fully in control of the area. There may be some resistance, but we are fully in this area," he said.

The Liberation Tigers of Tamil Eelam, as the rebels are known, have been fighting since 1983 for a separate homeland for 3.2 million predominantly Hindu Tamils, who have endured decades of discrimination by the dominant 14 million Sinhalese, most of whom are Buddhist.

The conflict — one of Asia's longest running and known for the Tigers' use of suicide bombers — is estimated to have killed about 65,000 people before the cease-fire.

Violence dropped sharply after the truce was signed, but sporadic shootings and bombings began escalating a year ago and the past six weeks have seen heavy fighting in some areas.

Both sides, however, insist they are abiding by the truce. But rebels warned Monday that if a Nordic monitoring mission in place since the cease-fire ruled that the government offensive violated the truce, the Tigers would consider themselves back at war.

"If they say it's a full-scale war, then we don't have to be bound by the cease-fire agreement," said Elilan, the rebel commander in the east.

The military has been trying for more than a week to take Sampur, which is near the port of Trincomalee, a key government naval base. The battle has killed at least 100 combatants and driven thousands of civilians from their homes.

Rebels had been using Sampur to fire howitzers and mortars at Trincomalee, which is the maritime lifeline for 43,000 soldiers stationed in Jaffna, a government stronghold in the island's predominantly Tamil north.

The Tamils held Jaffna until 1995 and claim it as their ancestral capital. They control all the land routes into the city, and the government had long wanted to retake Sampur to secure Trincomalee's port.

The apparent retaking of Sampur is the first strategic territorial victory for the army since hawkish Lt. Gen. Sarath Fonseka was appointed commander in December.

"Our armed forces have captured Sampur," President Mahinda Rajapakse told a meeting of his ruling party Monday, reportedly to thunderous applause.

But the Tigers still control wide swaths of Sri Lanka's north and east. And analysts said the army's push on Sampur could bring insurgent retaliation in relatively peaceful areas, like Colombo, the capital where the rebels have repeatedly set off suicide and roadside bombs.

"In the past ... the (rebels) have hit back ferociously," said M.R. Narayan Swamy, an analyst in New Delhi who has written extensively on the Tamil Tigers.

Police said they found hundreds of sticks of explosives in a truck that was trying to enter the Sri Lankan capital late Monday night.

Police discovered the 498 sticks of gelignite -— an explosive similar to dynamite — during a random search of vehicles entering Colombo from Nawagamuwa, north of the capital, senior superintendent K. Udayapala told The Associated Press.

Six people were being questioned, he said, offering no further details.

Heavy fighting erupted in late July over a rebel-controlled water supply near Trincomalee. It then spread to other parts of the east and north. There are no hard figures on the number deaths in the fighting, with estimates ranging from a few hundred to well over a thousand.

This year's violence has forced at least 220,000 people from their homes, the United Nations says, adding to the more than 600,000 people already displaced by fighting before the cease-fire and the 2004 Indian Ocean tsunami.

Most are living in squalid refugee camps in the north and east where food and medicine is running low because traffic across rebel and government lines has been curtailed. The fighting has also forced aid groups to scale back and in some cases cut off projects.