COLOMBO, March 30, 2008 (AFP) - Sri Lankan troops killed four Tamil Tiger rebels in weekend clashes in the embattled north, where soldiers were battling tropical illnesses brought on by heavy rains, the defence ministry said Sunday.

Security forces clashed with the Liberation Tigers of Tamil Eelam (LTTE) in the northern district of Vavuniya on Saturday, killing four rebels, the ministry said, adding that no soldiers were lost.

Government troops have killed at least 2,422 rebels since the beginning of January, while only 147 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 check the epidemic.

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.