COLOMBO, March 30, 2008 (AFP) - Fighting between Sri Lankan troops and Tamil Tiger rebels killed 36 combatants in the north, where soldiers were battling tropical illnesses brought on by heavy rains, the military said Sunday.

Security forces clashed with the Liberation Tigers of Tamil Eelam (LTTE) in the northern district of Vavuniya, Mannar and Jaffna on Saturday, killing 33 rebels, the defence ministry said.

The military said three soldiers died and at least 15 were injured in weekend fighting.

Sri Lankan airforce fighter jets on Sunday carried out sorties over a suspected rebel sea base in the guerrilla-controlled areas in the north, the defence ministry said.

Government troops have killed at least 2,451 rebels since the beginning of January, while 150 government soldiers have died in action, according to defence ministry figures.

Casualty numbers given by both sides cannot be independently confirmed as Colombo bars journalists and rights groups from frontline areas.

There was no immediate comment from the LTTE, who have waged a fight for autonomy in the island's north and east since 1972. Tens of thousands of people have been killed in the conflict.

However, a pro-rebel website, Tamilnet.com, said the guerrillas had beaten back an army offensive on Saturday in Vavuniya district.

Meanwhile, Sri Lankan troops have been hit by tropical illnesses as a result of heavy rains and floods in the north. Military spokesman Brigadier Udaya Nanayakkara said urgent measures had been taken to combat the problem.

The Sunday Times newspaper said that about 500 troops affected by dengue fever and the mosquito-borne chikungunya virus were being treated at hospitals in the island's northeast.