COLOMBO, Sri Lanka (AP) -- Tamil Tiger rebels launched an air and ground assault on a military complex in northern Sri Lanka early Tuesday, in an attack that killed 11 troops, one civilian and 10 of the assailants, the military said.
The military said it shot down one of the rebels' small planes following the attack.
The brazen operation targeting the base in Vavuniya was the first major rebel attack in government-held areas since the military began capturing large swaths of rebel-held territory in the north in recent weeks. The military offensive has forced the rebel fighters to retreat deep into the jungles and led to speculation that the rebels might be nearing defeat after 25 years of civil war.
The attack on the complex in Vavuniya, a city bordering rebel-held areas, began about 2:50 a.m. when the Tamil Tigers launched an artillery barrage, said military spokesman Brig. Udaya Nanayakkara. The complex houses headquarters for police, army and air force troops engaged in the battle against the rebels.
Soon after the first artillery shells exploded, a rebel ground assault team invaded the army base. About 3:30 a.m., two light aircraft from the Tamil Tigers' rudimentary air force joined in the attack, dropping two bombs on the army camp, he said.
The military drove off the planes with anti-aircraft fire and fighter jets followed them back to rebel-held territory, Nanayakkara said. One of the jets shot down one of the planes with a missile over the rebel stronghold of Mullaituvu, he said.
The artillery barrage - which totaled 70 shells - did not end until nearly 6 a.m., he said.
The attack killed 10 soldiers, one police officer and one civilian, Nanayakkara said. Troops killed 10 of the guerillas who had invaded the base, he said.
Hours later, air force fighter jets pounded a Tamil Tiger base deep in the rebel stronghold of Kilinochchi, said air force spokesman Wing Commander Janaka Nanayakkara.
He said the attack caused heavy damage to the base, which is believed to hold arms and ammunition.
With communication all but cut with the rebel-held areas, rebel spokesman Rasiah Ilanthirayan could not be reached for comment.
Independent verification of the fighting is difficult to obtain because most journalists are banned from the war zone. Both sides routinely exaggerate enemy losses and underreport their own.
The rebel-allied Web site TamilNet said there was no immediate indication a rebel plane was downed.
The combined assault on the Vavuniya base was reminiscent of an attack last year on an air base in the northern city of Anuradhapura that destroyed eight aircraft and killed 14 troops and 20 rebels.
As the fighting raged on, the United Nations announced it would begin withdrawing its staff from rebel-held areas this week after a government decision banning foreign aid workers from the area.
The U.N. said in a statement Tuesday that it had not yet set a timetable for the full withdrawal of its staff, but would continue trying to "address the humanitarian needs" of civilians in the area.
Many aid workers say their efforts at feeding and housing some of the 160,000 displaced civilians in rebel areas was crucial to staving off a humanitarian crisis.
Meanwhile, infantry battles across the north killed 15 rebels Monday, the military said in a statement.
The rebels have been fighting for an independent state in the north and east since 1983, following decades of marginalization of ethnic Tamils by governments dominated by the Sinhalese majority. More than 70,000 people have been killed in the conflict.
The government has vowed to crush the rebels seize their de facto state in the north by the end of the year.
The new round of fighting has forced tens of thousands of civilians to flee deeper into rebel-held territory.