Security forces set up snap roadblocks and checkpoints in the capital, Colombo, and prevented heavy vehicles from passing key government buildings amid fears the rebels could try to mark "Black Tiger" day with a bombing.

"Measures are under way to heighten our alert during the Black Tiger week," said Senior Deputy Inspector General Jayantha Wickramaratne, a police spokesman.

"We are taking all measures to eliminate the risk of terrorist attacks," he said.

The Liberation Tigers of Tamil Eelam (LTTE), who have been fighting for a separate homeland since 1972, have frequently staged their trademark suicide attacks around religious services for the fallen "martyrs."

The group's first suicide attack was by a guerrilla known as Captain Miller, who drove a truck bomb into an army camp on the Jaffna peninsula on July 5, 1987, killing 40 government soldiers.

The pro-rebel Puthinam.com website said 322 members of the elite Black Tiger suicide units had perished in attacks and that the group had deployed 61 suicide bombers in the past year alone.