KOLKATA: A seven-year-old child was killed and nine people, including his mother, were injured in a low-intensity explosion in front of a multi-storey building at Nagerbazar in Kolkata's northern suburbs on Tuesday, police said.The ruling Trinamool Congress held the BJP responsible for the blast and alleged that the saffron party was aiming to kill South Dum Dum Municipality chairman and TMC leader Panchu Roy. But the BJP rubbished the charges.As per the initial investigation, ammonium nitrate was used in the low-intensity blast outside a fruit shop on the ground floor of the building in the congested Kazipara area under the jurisdiction of Dum Dum police station around 9 am, Deputy Commissioner of Police, Barrackpore Commissionerate, Ananda Roy said."A child, who was severely injured in the blast, died in hospital. A total of nine persons are injured," he said.A police officer said, "It was a socket bomb explosion. A forensic team and the bomb squad of CID are examining the spot. We have started further investigation." A socket bomb is an improvised explosive device "Initially, we thought it was a gas cylinder blast. But it is not so. We have found a few iron nails but there is no smell of gunpowder," another senior police officer said.Panchu Roy, whose office is at the building, claimed that he was the target of the blast.Stopping short of naming any political party, he said the forces, which are currently attacking the ruling TMC all over Bengal, were behind the attack."It was a pre-planned blast... They had planned to kill me and other TMC workers, as it would create panic and help them gain a foothold in the area," Panchu Roy told PTI.Asked whether the explosion was a result of infighting within the TMC, he said there was no such issue in south Bengal.TMC North 24 Parganas district president and state minister Jyotipriyo Mullick, who visited the spot, held the BJP responsible for the blast and said it was aimed to harm Panchu Roy and other party members."The blast is an example of a deep conspiracy to kill Panchu Roy. This was a very well-planned one. It was a ploy to kill Panchu Roy. They (the BJP) is trying to create unnecessary problems among the people throughout the state."The BJP is trying to play divisive politics. They are shouting against the incident in Islampur but trying to kill Roy here," Mullick said.Two students died in a clash with the police at Islampur in North Dinajpur district on September 20 over the appointment of Urdu and Sanskrit teachers at Daribhita High School.The state government has ordered CID inquiry into the incident. BJP had called a state-wide shutdown over the incident on September 26.BJP state president Dilip Ghosh rubbished Mullick's allegations and said it has become a "mania" for the TMC to blame the saffron party for every incident that happens in the state.He alleged that the TMC party offices have become a "storehouse of bombs" and hence in every blast the name of the ruling party surfaces.