Four persons have been arrested in the case of a bomb blast at a school in West Bengal's North 24 Parganas district.?

A bomb exploded in Titagarh Free High School in Bengal's North 24 Parganas district on Saturday, damaging the roof the building. The school was in session when the bomb exploded. No casualties were reported.

The four accused were picked from Kamarhati and Titagarh areas around midnight, said a senior Barrackpore Police Commissionerate officer, adding they are aged between 18-19.

"We are trying to explore all possible aspects by interrogating them. One of the arrested hails from Kamarhati while the rest are from Titagarh," said the officer.

The preliminary investigation has revealed that three of the four accused are former students of the school and personal enmity with some other students is believed to be the motive behind the blasts. It also revealed that the accused had changed their initial plan to hurl a powerful crude bomb at the school gate, as the spot was crowded.?

The officer quoted above said the accused climbed onto the roof of an adjacent building to carry out the act.

He added that 10 crude bombs were found during a search operation at the residence of one of the accused.?

The Bharatiya Janata Partya (BJP) lashed out at Mamata Banerjee's Trinamool Congress (TMC) government over the blast and accused it of lawlessness and inaction over such incidents.?

"There have been several bomb blasts in this area before, but the police never played a positive role. The miscreants are gaining courage due to the Mamata government's dishonesty. Children are no longer safe at school," said BJP National Vice President Dilip Ghosh on Twitter on Saturday.

Ghosh further said that Saturday's blast points to the fact that "even school students cannot feel safe in Bengal".

"The education sector has begun its final journey in the state under the Trinamool Congress rule. Youths are roaming around with pistols and bombs as there are no jobs in West Bengal," Ghosh claimed.

Countering him, TMC MP Sougata Roy said the police is doing its job, and investigation is underway.?

"This should not be politicised by the BJP, which patronises miscreants," said Dumdum MP Roy.

On Saturday, BJP's Hooghly MP Locket Chatterjee demanded a Central Bureau of Investigation (CBI) probe into the blast.

(With PTI inputs)