COLOMBO: Suspected Tamil Tiger rebels killed four Sri Lankan soldiers and two aid workers in an ambush on Monday, the army said, hours after international envoys visited the rebels ahead of talks in Switzerland next week.

Violence has risen sharply in the past week and international ceasefire monitors say they fear that the upcoming talks – seen as key to averting a return to the island’s two-decade civil war – and even the 2002 truce could be in jeopardy.

“It’s a claymore attack,” said army spokesman Brigadier Prasad Samarasinghe, adding that the army suspected the rebels. “Four soldiers are dead, two are wounded. They were patrolling in a vehicle.”

International Catholic aid agency Caritas’ Human Development Centre in Jaffna said one of its vehicles had also been caught in the blast and that two Sri Lankan staff working on tsunami relief programmes had died and one was seriously wounded.

An army spokesman confirmed two aid workers had died, but said he had no details. The attack is the worst on land since the two sides agreed in January to hold their first direct talks since 2003. The rebels and government are due to meet in Geneva between April 19 and 21 for the next round of discussions, but the Tigers have yet to say for certain if they will attend.

A string of suspected Tiger attacks in December and January pushed the country to the brink of war.