COLOMBO (Reuters) -- Suspected Tamil Tiger rebels ambushed a truck carrying troops in northern Sri Lanka on Tuesday, killing one soldier and injuring three others with a roadside bomb, the military said.

The attack comes two days after peace talks between the government and Liberation Tigers of Tamil Eelam (LTTE) collapsed in Geneva, triggering fears of a deepening civil war.

The foes were locked in heavy artillery and mortar bomb duels in the north and east on Monday.

"A group of soldiers were heading on leave in (the northern district of) Vavuniya. The LTTE detonated a Claymore mine. Definitely it was them. One soldier got killed," a military spokesman said.

The talks ended on Sunday with both sides unable even to agree on whether or not to meet again for talks in the future, prompting mediator Norway to appeal to both sides to take time to reflect and not draw hasty conclusions.

The Tigers said their reclusive leader, Velupillai Prabhakaran, would outline the rebels' game plan during his annual "Heroes Day" speech due in November.

"The Sri Lankan government is going to bring another genocidal war on our people after stopping the work of the SLMM (Nordic truce monitors) on some false pretext," Tiger political wing leader S.P. Thamilselvan told a news conference in Geneva.

"Our people will wage the struggle to free themselves under our leader's direction," he added.

The collapse of the talks was the worst-case scenario for many analysts, diplomats and residents, who now fear a resumption of late July's heavy fighting that left hundreds dead, the worst violence since a 2002 ceasefire.

Sri Lanka's two-decade civil war has already killed more than 65,000 people since 1983.

The talks were deadlocked over a rebel demand that the government reopen the main north-south highway that crosses through rebel territory to Jaffna, which is cut off from the rest of the island by Tiger lines and where food supplies are scarce.

The government refuses, saying rebel artillery fire makes the road unsafe. Analysts say the closure is also curbing rebel movement and their revenues.

Tiger tax collection across their shared "border" with government territory is an important source of rebel funding.