Three persons were killed and six others injured after a blast at a passenger train in Pakistan's Balochistan area on Sunday, police said.District Police Officer Irfan Bashir said that suspected miscreants planted an improvised explosive device at the rail track to target the Jaffar Express, the Dawn reported.As the train, coming from Rawalpindi to Quetta, reached Dera Murad Jamali Station, there was a huge blast which damaged a portion of the track, he added.Investigation is underway, police said.