Police sources said the blast happened inside the washroom of the passenger train when the train reached Chichawatni.The train was traveling from Quetta to Rawalpindi. Soon after the incident was reported, rescue services reached the incident site and provided aid to the injured.The cause of the explosion is under investigation by law enforcement agencies.In January, at least eight people were injured on the same train after a blast in a bogie. The explosion damaged two bogies of the train as well as the railway track.Train service was suspended after the blast due to which women, children and elderly people faced difficulties. Security was tightened at the spot to avoid any other untoward incident.This incident took place three days after a 12-inch gas pipeline was blown up in the mountains of the Bolan district, causing suspension of gas supply to the provincial capital of Quetta and other areas of Balochistan.