A bomb explosion on a railroad track derailed a passenger train Monday shortly after it was attacked by gunmen in southwestern Pakistan, police and rail officials said. There were no immediate reports of injury.

The blast blew up a portion of the track, sending the train's engine and two cars off the rails as it approached a railway station in the village of Hasipur, about 50 miles southeast of Quetta, said Gul Khan Sasoli, a senior police official.

Only 50 passengers were on the train when it derailed 15 minutes after gunmen attacked it with assault rifles in a mountainous region, Sasoli said.

Bullets hit the train but did not strike any of the passengers, said Ghulam Rasool, traffic controller at the state-run Pakistan Railways. Security forces deployed in the rugged area to protect the railway line returned fire, he said.

No one immediately claimed responsibility for the shooting and bombing.

The train was headed from Quetta, capital of Baluchistan province, to Lahore in eastern Punjab province when it was attacked.

In another attack in the region, two bombings blew up a section of a track southeast of Quetta, Sasoli said. No one was injured in the explosions, but gunmen shot at a train and a paramilitary pickup going to the scene to do repairs, injuring two railway workers and three soldiers, he said.

Sparsely populated Baluchistan has been wracked by small-scale bombings and rocket attacks in recent years, most blamed on tribesmen demanding increased royalties for resources extracted from the province.