A crude bomb exploded on the roof of a school building in West Bengal's North 24 Parganas district on Saturday when classes were in progress, a senior police official said.

There was no casualty in the incident as students and teachers were in rooms located on the first two floors of the three-storied building, he said.

The students got panicked hearing the sound of the explosion and left the premises helter-skelter, while teachers went upstairs to find bomb splinters close to the roof, according to a managing committee member of the state-aided institute at Titagarh in the industrial belt of the district.

A top official of Barrackpore Police Commissionerate told reporters after visiting the spot that the blast was caused by a single crude bomb.

He said that it would be investigated whether the bomb was hurled from a nearby building or it had been kept there and suddenly went off.

Barrackpore MP Arjun Singh told reporters at the spot that whoever was responsible for the blast would have to be arrested and punished.

"Had any child been around the spot, I shudder to think what could have happened. I have urged the commissioner of police and other top officials of Barrackpore Police Commissionerate to find out the culprits," said Singh who returned to the TMC from the BJP last May.

BJP's Hooghly MP Locket Chatterjee demanded a CBI probe into the incident.

"Even school children are not safe in the rule of Mamata Banerjee. Bombs are discovered in houses and party offices across West Bengal. Today's incident is a pointer to the grim law and order situation. We don't have faith in the state police or CID. We want CBI probe to unravel the truth," she said.

When asked to comment on Chatterjee's claims, I don't want to join the issue with her. Let the police investigate the case first.