Government forces and Tamil Tiger separatists fought pitched battles in the rain and mud in a ring of villages outside the rebel administrative capital in northern Sri Lanka, the military said Tuesday.

The government has vowed to destroy the rebel group by the end of the year and has pushed deep into the rebels' de facto state in the north in recent months. Several weeks ago, the military said it was just outside the rebel headquarters at Kilinochchi and was poised to seize the town from the rebels.

But monsoon rains, which began more than a week ago and are expected to last for months, have made the fighting more difficult and bogged down many of the military's vehicles, said a military official, who spoke on condition of anonymity because he was not authorized to speak to the media.

On Monday, heavy clashes raged throughout the day in three villages near Kilinochchi, the military said in a statement.

The military did not provide casualty details in line with a new government policy, but said troops inflicted heavy losses on the rebels.

Fighting also broke out Monday in nearby Mullaitivu district, the military said.

It is not possible to obtain independent accounts of clashes because most journalists are barred from the war zone. Rebel spokesmen could not be reached for comment because their communication lines have been severed.

Meanwhile, police said unidentified gunmen fatally shot four members of a pro-government militia in the volatile east on Monday night. A rebel-affiliated Web site said Tamil Tiger fighters were behind the attack.

The shooting took place at a political office of the Tamil Makkal Viduthalai Pulikal militia near the town of Batticaloa, said police spokesman Ranjith Gunasekara.

The militia broke away from the Tamil Tigers and has formed an alliance with the government.

Gunasekara said another five militia members were missing and police were investigating who was behind the attack.

The group was formed in 2004 when a former rebel commander defected from the Tamil Tigers with thousands of his men. The group helped the government push the rebels out of the east last year.

The TamilNet Web site said "Tiger commandos" launched the attack on the "paramilitary camp," seizing weapons and destroying it. The Web site, citing rebel sources, said the rebels had kidnapped six militants.

The Tamil Tiger rebels have fought since 1983 to create an independent state for ethnic minority Tamils, who have suffered marginalization at the hands of successive governments controlled by ethnic Sinhalese. The conflict has killed more than 70,000 people.