At least 15 people were killed and several others injured when gas cylinder exploded in a passenger bus in Islamabad on Tuesday. According to report the ill-fated bus was heading toward Kalar Sayda from Peer Widhayi bus stand. Sources said that the incident took place near Kral chowk. The dead and injured were shifted to PIMS Hospital. Police and rescue workers rushed to the spot and cordoned off the area. Bomb disposal squad have also reached the area to ascertained whether the blast was of cylinder or a sabotage. Eyewitnesses said the bus caught fire following the blast, killing 15 and burning several others.