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.
The police however, did not provide any other details of the blast which comes four days after the serial Easter Sunday bombings that killed 359 people and injured hundreds others in the bloodiest day in Sri Lanka since the end of the civil war a decade ago, reports Xinhua news agency.
Sri Lankan government on Wednesday admitted that 'major' intelligence lapses led to the horrific Easter Sunday blasts.
In the Easter Sunday bombings, hundreds of others were also injured in what is being called as the bloodiest day in Sri Lanka since the end of the civil war a decade ago.
Nine suicide bombers, including a woman, were involved in the massive terror attacks, and 60 people have been arrested so far for suspected involvement.
The Sri Lankan government has blamed a local Muslim outfit, National Thowheed Jamath (NTJ), for the deadly bombings.
Islamic State had claimed responsibility for the terrorist blasts in Sri Lanka.