At least three people were killed and 12 wounded when a passenger train hit a bomb planted on a railway track in southwest Pakistan on Sunday.

At least three people were killed and 12 wounded when a passenger train hit a bomb planted on a railway track in southwest Pakistan on Sunday, officials said.

The bomb exploded when the train reached Mastung, a district in Pakistan's insurgency-hit southwestern Baluchistan province.

"The bomb was planted on the railway track. It exploded when the train reached Dasht area (part of Mastung)," Shafqat Anwar, a senior government official on site said.

Anwar said the Jaffar Express was travelling from Quetta, the main town of Baluchistan, to the garrison city of Rawalpindi in central Punjab province. One passenger wagon was damaged after it was derailed by the impact of the blast.

"At least three passengers have been killed, two on spot while another succumbed to his injuries on his way to hospital," Anwar said.

Anwar Sammo, another senior government official, told AFP that an IED (improvised explosive device) was used in the attack.

"The IED was planted on the railway track. All those killed and injured were railway employees," Sammo told AFP, adding that some 650 passengers were travelling in the train.

No group has yet claimed responsibility for the attack but Baluch separatists demanding greater autonomy have been waging an insurgency for years and the province is also driven by sectarian strife and extremist violence.