Sri Lankan forces fought their way into the Tamil Tiger rebels' final stronghold of Mullaittivu on Sunday and were battling to take control of the town, the military said.
The capture of Mullaittivu would expel the rebels, who once controlled a wide swath of northern Sri Lanka, from the last major town under their control and could force the insurgents remaining in the nearby jungles to abandon their conventional tactics in favor of guerrilla warfare.
In recent weeks, the Sri Lankan military has captured the rebels' administrative capital of Kilinochchi and forced them into a broad retreat and boxed them into a tiny pocket of territory in the northeast.
Independent analysts estimate that thousands of fighters remain holed up in the jungle with hundreds of thousands of civilians, many of them war refugees repeatedly displaced by the fighting.
On Sunday afternoon, troops pushing toward Mullaittivu from the south entered the city, said military spokesman Brig. Udaya Nanayakkara.
"They are in Mullaittivu," he said, noting they had not yet taken control of the city.
"Troops are negotiating pockets of fighting here and there," he said.
Rebel officials could not be reached for comment because communications to the northern war zone have been cut. It is impossible to verify the military's accounts because independent journalists are barred from the area.
Defence spokesman Keheliya Rambukwella described the town as the rebels' last bastion and main operations center.
The rebels took control of the town in 1996 when they overran a military camp there and killed nearly 1,000 soldiers.
The troops' entrance into the town after 13 years came after the government ordered all government-paid administrators in the rebel-held north to leave the territory in preparation for a final assault on the insurgents.
The Tamil Tiger rebels have fought since 1983 to create a separate state for ethnic minority Tamils who have suffered decades of marginalization at the hands of successive governments controlled by the Sinhalese majority. More than 70,000 people have been killed in the violence.
The government of President Mahinda Rajapaksa has vowed to destroy the group and end the war. In recent fighting, it has broken through the rebels' defenses in the north and forced them into a major retreat.
Human rights groups have expressed growing concern in recent weeks for the safety of the hundreds of thousands of civilians reportedly living in the shrinking rebel-held area.
The groups have accused the Tamil Tigers of preventing the civilians from fleeing the war zone, while the government has said the rebels hoped to use the civilians as human shields. Reports of civilian casualties in the area have grown in recent weeks.
Last week, the government declared a 13.5 square mile (35 square kilometer) "safe zone" on the edge of the rebel-held area and called for civilians to gather there.
The government then ordered its administrators, who coordinated social services inside the rebel areas, to leave the region, Rambukwella said.
The administrators also helped distribute international food aid sent to the civilians in the area.
"We believe the remaining area (outside the 'safe zone') is left with only terrorists and they don't need to be administered by the government," he said.
Rambukwella did not explain how the food distribution would be handled in their absence.