— A passenger train derailed Monday in Pakistan’s restive Baluchistan province when a bomb detonated next to it, killing at least seven people, officials said.

The Jaffar Express train was traveling from Rawalpindi to Quetta when the attack occurred mid-morning, about 300 miles from its destination.

Riaz Ahmed, a railway police officer in Quetta, said the bomb had been planted on the tracks. But Pakistan’s railway minister, Khwaja Saad Rafiq, told local news media that authorities also are investigating whether a suicide bomber could be to blame.

Seven passengers, including three brothers traveling together, were killed, and at least a dozen others were injured, Ahmed said. Four train cars flipped when the bomb detonated, he added.

There was no assertion of responsibility for the bombing, but Pakistan’s military has been battling separatists for years in resource-rich Baluchistan.

In 2011, another Quetta-bound train derailed in the southwestern province after a remote-
controlled bomb exploded. The Baluch Republic Army, a militant group fighting for secession that has been banned by Pakistan’s government, asserted responsibility for that blast. At the time, the group vowed that such assaults would continue.

But attacks on trains in Pakistan extend beyond Baluchistan, where officials are still trying to recover from a 7.7-magnitude earthquake last month that killed more than 500 people.

In August, a bomb detonated on a passenger train in the Punjab province en route from Lahore to Karachi. Three people were killed in that attack. A train heading from Karachi to Peshawar was targeted in a bombing in 2012 that killed two passengers, according to the Express Tribune newspaper.

After Monday’s bombing, train service to and from Quetta was suspended pending a security review, said Ahmed, the railway police officer.

“This was a cowardly attack and an act of terrorism,” Rafiq, the railway minister, told reporters.