A police officer and rescue workers stand near to a derailed passenger train, after a bomb went off on track in Naseerabad, Pakistan, on Sunday. Khalid Hussain /Reuters

QUETTA (Pakistan): At least four people were killed and seven injured when a remote-controlled bomb exploded on a railway line in southwest Pakistan as a passenger train was passing by, police said.

The incident occurred in the troubled province of Balochistan, 311 kilometres (194 miles) southeast of the provincial capital Quetta.

"The train was going from Quetta to Rawalpindi when it came over a remote-controlled bomb and four people were killed while seven others were injured," senior police official Irfan Bashir told the media.

"Three carriages of the train also went off the track and rescue work is under way," he said.

The incident was confirmed by another senior police official, Rao Munir Zia.

No group has claimed responsibility for the attack.

Balochistan, which borders Afghanistan and Iran, is Pakistan's largest and poorest province, rife with ethnic, sectarian and separatist insurgencies.

Its residents have long complained that it does not receive a fair share of the profits made from its mineral wealth.

Agence France-Presse