A blast was heard on Thursday from vacant land behind the magistrates court in the town of Pugoda, 40 km (25 miles) 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.

Sri Lankan government on Wednesday admitted that 'major' intelligence lapses led to the horrific Easter Sunday blasts.

Islamic State had claimed responsibility for the terrorist blasts in Sri Lanka.