COLOMBO, Sri Lanka - Sri Lankan forces sweeping down from the north captured an important Tamil Tiger base on the Jaffna peninsula Thursday, further boxing in the retreating rebel group, the military said.

The capture of Pallai on the narrow isthmus connecting Jaffna with the rest of the island nation came after the rebels reportedly withdrew much of their artillery and heavy weaponry from the peninsula into their jungle strongholds to the south.

Analysts said the group appeared to be sacrificing its bases on the peninsula and consolidating its forces in the Mullaittivu area, where it will likely make a stand against the government.

The rebels were not available for comment Wednesday; most communications in their region have been severed. Independent accounts of the fighting were not available because the government has barred journalists and foreign aid groups from the war zone.

The new fighting kept up the pressure on the beleaguered rebels a day after the government officially banned the group, ruling out the resumption of any peace efforts in the foreseeable future.

Sri Lankan forces have broken through the rebels' defenses in recent months, seizing huge chunks of rebel-held lands, capturing their administrative capital of Kilinochchi and trapping the insurgents in a tiny section of the northeast.

Government officials say they aim to crush the group and end this Indian Ocean island nation's 25-year-old civil war.

For more than a decade, the rebels have run a de facto state, squeezed between the government-held Jaffna peninsula -- the northernmost point in the country -- and the rest of the island to the south.

While government troops pushed deep into rebel territory from the south, troops in the Jaffna peninsula had been unable to break open the Tamil Tigers' heavily fortified northern lines until earlier this week when they overran the front at Muhamalai.

Those force pushed southward about five kilometres, capturing Pallai, military spokesman Brig. Udaya Nanayakkara said.

"There have been small pockets of (rebels) and they have engaged moving troops, but after giving final resistance they moved toward Elephant Pass," he said, referring to a strategic rebel base on the southern point of the isthmus.

In other fighting, air force jets attacked two rebel boats that were camouflaged and anchored in a lagoon in the north Thursday morning after pounding a group of rebels late Wednesday who appeared to be working to construct new defense fortifications.

The attacks came after the Cabinet voted unanimously Wednesday night to officially outlaw the Tamil Tigers, ruling out the possibility of restarting peace talks anytime soon.

The decision followed the rebels' rejection of a government ultimatum to allow hundreds of thousands of civilians living in rebel-held areas to leave, Cabinet minister Maithripala Sirisena said.

The government and international rights groups have accused the Tamil Tigers of holding civilians as human shields against the military offensive. The rebels deny the charge.

Government officials already have vowed to destroy the rebel group, so while Wednesday's ban was little more than a formality, it was seen as a symbolic rejection of any possible rapprochement.

The rebels 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.

The Tamil Tigers have been outlawed before, but the government lifted the ban in 2002 when the sides agreed to a cease-fire. The deal collapsed amid new fighting three years ago.