Tamil Tiger rebels launched fresh attacks overnight on key military targets in northern Sri Lanka, where a week of fierce fighting killed more than 800 rebels and security forces, the military said Thursday, as the country spiraled closer to all-out war.

The stepped-up attacks Wednesday in northern Jaffna Peninsula came as Sri Lanka's president vowed the government would not bow to insurgent demands and withdraw from the north, claimed by Tamil Tiger rebels as the heartland of ethnic Tamil culture.

Twenty boats from the Tiger's feared sea unit attacked a strategic land and naval base in northern Kilaly, off the west coast of Jaffna Wednesday night, prompting a gunbattle that lasted until dawn, military spokesman Maj. Upali Rajapakse said.

CountryWatch: Sri Lanka

He said the navy sunk three rebel boats, and killed 70 rebels, who had also attacked by land. He said about 15 soldiers and sailors had been killed.

The Tigers could not immediately be reached to confirm the report, but each side routinely disputes the accounts — and death tolls — offered by the other, and it is virtually impossible to verify their claims with the area largely closed off by the violence.

The fighting took place off Jaffna Peninsula, about 300 kilometers (186 miles) north of Colombo, which is controlled by the government but claimed by the rebels as the heartland of Tamil culture. Since Aug. 11 they have stepped up efforts to retake the peninsula in fighting that has killed at least 700 rebels and 106 government troops, Rajapakse said.

He said between another 500 to 600 rebels and about 170 government forces had been wounded in the fighting, which is the fiercest the area has seen since a 2002 cease-fire.

Also in Jaffna, insurgents fired a barrage of rockets and artillery at an air base on Wednesday night and Thursday morning, the pro-rebel TamilNet Web site said, adding that the Tigers may have hit a military helicopter that was about to take off.

On Wednesday, the government launched air strikes on northern territories held by the rebels, who have been fighting for over two decades for a separate homeland for the country's 3.2 million minority Tamils in the north and east.

Government forces, meanwhile, fired on rebel-held areas in Muttur, a Muslim town south of the eastern port of Trincomalee, near where fighting broke out in late July over a rebel blockade of a water supply, the Web site reported.

The two sides have for weeks traded artillery and mortar fire in the area, from which tens of thousands of civilians have fled.

Norway brokered a 2002 cease-fire between the rebels and government, which is dominated by representatives of Sri Lanka's 14 million predominantly Buddhist Sinhalese. The Tamils are largely Hindu.

Although the truce remains officially in effect, violence has been rising for more than a year, and the open fighting in recent weeks in the north and east has pushed the South Asian nation toward a resumption of full-scale war.

Sri Lankan President Mahinda Rajapakse on Wednesday insisted that the government was not at war, and that the country had a right to defend its sovereignty.

He also vowed that the government would not withdraw from the north.

Aid workers have said that more than 100,000 people have been displaced by the fighting.