Suri: Police arrested seven persons in connection with the explosion at Trinamul office in Birbhum's Kankartala on Monday morning that flung the door and windows 35ft to 40ft away.

No one was in the office at the time of the blast, which was allegedly caused by crude bombs stocked inside.

A team of CID's bomb squad arrived on Tuesday and took samples from the debris for a forensic test, the police said.

The police have started a case in connection with the blast under the Explosive Substances Act and three out of the arrested seven were remanded in five days of police custody by a Dubrajpur court.

Sources in Trinamul said all the seven who were arrested in connection with the case were known Trinamul supporters in the area.

Trinamul district chief Anubrata Mondal had claimed after the explosion that BJP activists from Jharkhand had hurled bombs at the party office. But on Tuesday, Mondal declined to comment on the arrest of the Trinamul supporters. "I will not make any comment related to the explosion in the office," Mondal said.

Trinamul officially did not confirm that the arrested persons were from Trinamul.

BJP district president Ramkrishna Roy said: "The arrest proved who were behind the explosion."

The explosion had ripped through a Trinamul party office in Barrah.