COLOMBO (REUTERS) - A blast was heard on Thursday (April 25) from vacant land behind the magistrates court in the town of Pugoda, 40km east of the capital Colombo, police and local residents said.

Police said they were investigating the explosion, which came at a time of high tension in Sri Lanka following the Easter Sunday suicide bomber attacks on the island state that killed 359 people and wounded about 500.

"There was an explosion behind the court, we are investigating," police spokesman Ruwan Gunasekera said, adding that it was not a controlled explosion like other blasts in recent days.

There were no casualties, said Mr Gunasekera.

In another incident, the authorities lifted a security alert at the central bank in Colombo after it was locked down following a warning about an impending explosion, two bank sources said. Workers were allowed to leave the bank, the sources said.

The story is developing.