The Sri Lankan army accused the rebels of carrying out two attacks on Saturday with claymore fragmentation mines that killed seven servicemen and wounded several in the Tamil-dominated north and east.
In the more deadly of Saturday's explosions, an anti-personnel mine was possibly hidden in a parked farm vehicle and detonated as a bus full of government soldiers drove past in Vavuniya district, a military spokesman said.
"At least four soldiers were killed on the spot and 11 escaped with injuries," the spokesman said. A fifth died later of his wounds in hospital.
Four more Claymore mines, two of them in the same district, had been uncovered earlier in the day but they were defused by security forces before they exploded, he said.
The Liberation Tigers of Tamil Eelam (LTTE) said their withdrawal from talks in Switzerland - aimed at saving a faltering 2002 ceasefire - was due to problems with a requested safe-conduct transport of rebel commanders.
On Thursday, Norway won agreement from the Colombo government and the LTTE for a five-day delay to allow the Tigers more time to prepare for the discussions that would be a continuation of a round held in February.
A cycle bomb explosion killed 13
people on April 12 in Trincomalee
The talks were due to be held in Geneva on April 24.
The Tigers were concerned about Sri Lankan navy plans to monitor a boat that was to have taken the commanders based in the east and their Nordic escorts on Saturday to the Tigers' northern base, the head of the Tiger peace secretariat said.
"It is very important we meet our commanders," S Puleedevan told Reuters. "We have cancelled the transport. If we cannot meet them, Geneva is off."
The rebels also accused the military of carrying out an attack in their territory that they said killed one rebel and one rebel civilian supporter. Each denies the other's accusations.
Swedish Major-General Ulf Henricsson, head of the unarmed Sri Lanka Monitoring Mission tasked with monitoring the truce, said the Tigers had initially agreed to allow the navy to monitor the rebel vessel from a distance.
The government said they had provided what the rebels asked for and that the ball was entirely in the Tigers' court, but diplomats say the whole dispute could have been avoided if the government had agreed to a rebel request for a helicopter.
At least 50 people, mostly security personnel, have died in attacks in the past week in Sri Lanka, where over 60,000 people have been killed in three decades of ethnic bloodshed between the majority Sinhalese and minority Tamils.