At least 20 people were killed or wounded Thursday morning in a powerful bomb explosion in the northern Sri Lankan town of Vavuniya, informed sources said.

The sources said the bomb had gone off at the central post office in Vavuniya, about 260 kilometers north the capital of Colombo.

Rescue operations have been conducted to rush the wounded to the nearby hospitals, said the sources.

The bombing came despite tight security throughout the country amid fears of more bomb attacks by the separatist Liberation Tigers of Tamil Eelam (LTTE) rebels who are fighting for an independent homeland for minority Tamils in Sri Lanka's north and east since 1983.

The bomb attacks have been the trademark of the LTTE rebels who are blamed for a series of suicide bomb attacks in recent weeks against President Chandrika Kumaratunga and other senior officials. (Xinhua)