One person was killed and two others were seriously injured in an explosion at an office of the ruling Trinamool Congress at Makrampur in West Midnapore district, police here said. It was not immediately known whether a crude bomb had exploded or a gas cylinder inside the party office led to the incident, the sources said. The cause of the blast that took place at around 10 am would be known only after forensic examination, police said. The injured were admitted to a hospital where their condition was stated to be stable. The police remained tight-lipped whether the deceased and the injured belonged to the TMC. Police have cordoned off the explosion site. TMC district president Ajit Maiti said they were collecting all information regarding the explosion. "Either it was a cylinder blast or some outsiders threw bombs at the TMC office. We have requested the administration to investigate," he said. Local TMC MLA Pradyut Ghosh said the cause of the explosion could not be ascertained immediately and the police were looking into it.