Sri Lankan President Mahinda Rajapaksa says the country's forces have captured the strategic base of Elephant Pass from the Tamil Tiger rebels.

Rajapaksa said in a nationally televised address that the rebels' last base on the Jaffna Peninsula fell Friday afternoon to advancing troops.

The capture of the base gives the government nearly full control of the peninsula for the first time since 2000 and reopens a major highway to the once isolated government-held town of Jaffna, the Tamils' cultural capital.

It also boxes the rebels into a shrinking pocket of territory in the northeast around their last remaining stronghold of Mullaittivu.

The government, which seized the rebels' administrative capital of Kilinochchi last week, has promised to crush the rebel group and end this Indian Ocean island nation's 25-year-old civil war.

Meanwhile, the rebels detonated a roadside bomb in the country's east Friday that killed three air force troops and four civilians, military spokesman Brig. Udaya Nanayakkara said.

The attack outside the eastern city of Trincomalee signalled a return to guerrilla tactics. The government captured the east from the rebels in 2007, but attacks in the area have increased in recent months.

On Friday, government forces marching from the north and south broke into Elephant Pass, which is located on the isthmus connecting the northern Jaffna Peninsula with the rest of the island, a senior military official said, speaking on condition of anonymity because he was not authorized to talk to the media.

The troops were engaged in heavy fighting with the rebels, the official said before the capture.

Tamil Tigers officials were not immediately available for comment.

Analysts said the guerrillas appeared to have withdrawn their artillery and heavy weaponry from the area and were sacrificing their bases on the peninsula to consolidate forces near Mullaittivu, where they will likely make a stand.

Human rights groups have warned that casualties among the hundreds of thousands of civilians living in the shrinking pocket of rebel territory were likely to mount as the government closed in on the insurgents.

The Tamil Tigers have been fighting since 1983 to create an independent homeland for ethnic minority Tamils, who have suffered decades of marginalization by governments controlled by the Sinhalese majority. The conflict has killed more than 70,000 people.

Troops south of Jaffna were also fighting the rebels, pushing eastward from the Kilinochchi area, Nanayakkara said. The troops found the bodies of seven insurgents from fighting Thursday, he said.