A bomb blast on a train in Pakistan’s restive southwestern province of Baluchistan killed at least 13 people and injured 40 others on Tuesday, officials said, with the death toll feared to rise.

A bomb blast on a train in Pakistan's restive southwestern province of Baluchistan killed at least 13 people and injured 40 others on Tuesday, officials said, with the death toll feared to rise.

The United Baluch Army (UBA), one of several armed separatist groups in Baluchistan, claimed responsibility for the bombing, with its spokesman warning of more such attacks in the coming days in response to a major military operation against militants that began on Monday.

The explosion occurred after the train had pulled to a stop and passengers were disembarking at Sibi railway station around 160 kilometres (100 miles) south of its destination Quetta, the provincial capital.

Two carriages quickly became engulfed by a scorching inferno and smoke as passengers, some of whom were on fire, screamed and struggled to escape, senior police official Mohammad Nazar, who was at the scene, told AFP.

"We have recovered 12 dead bodies from the train. They have been burnt to charcoal," he said, adding one of the injured had died after being taken to a military hospital in the same town.

Sher Khan Bazai, a senior administration official, confirmed the incident.

"24 patients are in critical condition, they will be shifted to Quetta as soon as they are stable enough to travel," he said, adding that the injured included six women and four children.

The flames were only put out after fire fighters reached the scene, Nazar told AFP.

"I can't say whether the dead are adults or children as they are beyond recognition," he said.