The six men were killed and another injured when their vehicle triggered a mine planted by suspected Tamil Tiger rebels in Jaffna, 400km north of the capital Colombo, an official said.

"The troops were transporting lunch for their colleagues when they were caught up in the explosion," a military official in the area said. "We believe it is the work of the Tigers."

The official said another soldier was killed in a Tiger attack overnight in the same area.

In other violence, one solider was shot dead Saturday in northern Sri Lanka while three civilians were killed in the eastern port city of Trincomalee on Sunday.

Sunday's blast was the worst against government troops since they entered a truce with the Tigers in February 2002.

A Norwegian-led truce monitoring panel, in a statement, expressed concern over the latest upsurge in violence and urged the government and the rebel Liberation Tigers of Tamil Eelam (LTTE) to calm the situation.

"We urge them and all other community leaders to use their influence to ensure that violence and attacks come to an immediate end," the Sri Lanka Monitoring Mission (SLMM) said.

"The SLMM warns that there is a real danger that these disturbances and hostilities can spread and result in irreparable deterioration of security and prevent any real restoration of normalcy in the affected communities."

The statement came after the LTTE put the new government of President Mahinda Rajapakse on notice last month to come up with a solution to the island's drawn out Tamil separatist conflict which has claimed over 60,000 lives since 1972.

The LTTE warned that they would next year begin their campaign for independence and set up a homeland unless there was a political settlement to their conflict.

The LTTE has been fighting for total independence in the island's northeast, but in December 2002 agreed to settle for extensive devolution of power under a federal system.

In recent weeks, there had been tension in the Jaffna peninsula, the former capital of the Tigers. Tensions heightened Friday after the killing of two Tiger rebels by unidentified gunmen.

The LTTE has accused the Sri Lankan military of supporting a breakaway faction. The Sri Lankan military denies the charges.

In the island's northeastern district of Trincomalee, police Sunday found three bullet-ridden bodies of Tamil civilians who had been taken away Saturday night by Tiger rebels, police said.

They said a fourth man escaped with serious injuries and was admitted to hospital.

Sri Lankan Tamils constitute about 12.6 percent of Sri Lanka's 19.6 million population, while Muslims, make up about 7.5 percent. The mainly Buddhist Sinhalese are the majority community.