New Delhi - At least 15 people were injured when a bomb detonated inside a passenger train in eastern India on Tuesday, police said.The explosion took place about 20km from Kolkata, following an argument between suspected criminals, an officer at the Barrackpore police control room said."Witnesses said a group of people got on the train at Titagarh. There was altercation between them and later a bomb exploded. Police are investigating what happened," Tushar Mandal said.The injured were admitted to nearby hospitals where the condition of two passengers was said to be critical.The man who was carrying the bomb was among the injured. He was found to have a criminal record, railway police said.