The Tigers were concerned about Sri Lankan navy plans to monitor a boat that was to have taken rebel commanders based in the east and their Nordic escorts on Saturday to the Tigers' northern base, said the head of the Tiger peace secretariat.

"It is very important we meet our commanders," S. Puleedevan said. "We have cancelled the transport. If we cannot meet them, Geneva is off."

In fresh violence, a powerful bomb exploded near a military base in northern Sri Lanka yesterday, killing at least four soldiers and wounding 12, military officials said.

An official said the bomb, which went off as a bus transporting troops passed by in the district of Vavuniya, may have been rigged up to a tiller parked on the road.

At least 50 people, mostly security personnel, have now died in attacks in the past week in Sri Lanka, where over 60,000 people have been killed in three decades of ethnic bloodshed.