Two days of heavy artillery and mortar fire killed more than 80 Tamil Tiger rebels, Sri Lanka's military said Saturday, as the United Nations warned of an impending humanitarian crisis in areas cut off by fierce fighting.

Sri Lanka's air force, meanwhile, destroyed a strategic rebel sea base in the north in overnight airstrikes, killing an unknown number of guerrillas, said military spokesman Maj. Upali Rajapakse. The rebels' deadly naval wing has carried out several suicide attacks against Sri Lanka's navy.

CountryWatch: Sri Lanka

Rajapakse said the sea base had been used to launch attacks on government positions in Jaffna Peninsula, which has seen some of the fiercest fighting since a 2002 cease-fire.

A pro-rebel Web site, Tamilnet, however, said the air force dropped four bombs on a boat-building yard that was part of a civilian tsunami reconstruction project, and that two workers were wounded. Rajapakse denied this.

It was not immediately possible to verify either side's claims as conflict areas in the north have been virtually cut off to outsiders, including media and aid agencies.

The two sides also routinely dispute claims — and death tolls — offered by the other.

The military said late Saturday more than 80 rebels had been killed in two days of intermittent shelling along their de facto border in Muhammalai in the north. The two sides exchanged mortar and artillery fire since Friday, the Media Center for National Security said on its Web site.

The U.N., meanwhile, announced only minimal aid has been able to reach tens of thousands of people who have been displaced by weeks of fighting in the north and east of the country.

The U.N. said it was "deeply concerned" about the humanitarian situation in Jaffna and other areas where the government has restricted access.

"Certainly we are deeply concerned about the water and food and sanitation problem," U.N. spokeswoman Orla Clinton said. "And if we don't get access, then yes, it will be a humanitarian crisis. Aid agencies need unconditional and immediate access."

On Saturday, the government said it would send 3,800 tons of food and other aid to Jaffna.

The Tamil Tigers have been battling the government for more than two decades for a separate homeland for the country's 3.2 million ethnic Tamils in the north and east, where they already control wide swaths of territory.

A Norwegian-brokered cease-fire in 2002 was supposed to end the violence, in which as many as 65,000 people were killed, many of them civilians targeted by rebels and security forces.

In the last six months, however, sporadic clashes between government troops and rebels along their de facto borders have escalated into what many here refer to as an "undeclared war."

Nordic truce monitors estimate about 1,500 people have died since the upsurge in violence since December.

The United Nations' refugee agency estimates about 170,000 people have fled their homes since April to escape the near daily exchange of artillery fire, and are now living in cramped, unsanitary conditions in churches, temples or out in the open.