Armed militants have attacked a train carrying more than 400 passengers in Pakistan’s Balochistan region and taken many of them hostage, military sources told the BBC on Tuesday.

The Baloch Liberation Army (BLA) opened fire on the Jaffar Express train as it was travelling from Quetta to Peshawar.

The separatist group said it had bombed the railway tracks before storming the train in the remote Sibi district, claiming the train was under its control.

Local media reported that at least 16 militants had been killed and 104 passengers had been rescued by Wednesday morning.

Among those rescued were 17 injured passengers who were receiving treatment in hospital.

Local reports said the militants had threatened to kill the hostages if authorities did not release Baloch political prisoners within 48 hours.

The rescue operation is ongoing.

A Balochistan government spokesman told the local newspaper Dawn on Tuesday that “heavy gunfire” had been reported on the train.

A senior police officer said it was “stuck in front of a tunnel surrounded by mountains”, AFP news agency reported.

A senior military official confirmed to the BBC that more than 100 military personnel were travelling on the train from Quetta.

Pakistani authorities – along with several Western countries including the UK and the US – have designated the BLA a terrorist organisation.

It has waged a decades-long insurgency for freedom and has carried out deadly attacks, often targeting police stations, railways and highways.

On Tuesday, the group warned of “serious consequences” if it tried to rescue those it was holding.

“I can’t find words to describe how we escaped. It was terrifying,” Muhammad Bilal, one of the freed hostages, told AFP news agency.

Another passenger, Aladitta, said he was allowed to travel because of his heart condition. The 49-year-old recalled how people “started hiding under seats in fear” when the attackers stormed the train.

A local railway official in Quetta earlier told the BBC that a group of 80 passengers – 11 children, 26 women and 43 men – managed to get off the train and walk to the nearest railway station, Paneer.

The official said the group was made up of locals from Balochistan province.

One man, whose brother-in-law was still on the train, described an agonising wait. He tried to get to the area but many roads were blocked.

Meanwhile, families of worried passengers gathered at the counter at Quetta railway station to seek information about their loved ones.

Muhammad Ashraf, the son of a passenger who had left Quetta for Lahore on Tuesday morning, told BBC Urdu that his father had been unable to be contacted.

Another relative said he was “crazy with worry” about his cousin and her young child, who were travelling from Quetta to Multan to pick up a family member.

“Nobody is telling me what will happen to them or if they are safe,” Imran Khan told Reuters.

Officials say they have not yet communicated with anyone on the train.

Officials told the BBC that the area has no internet or mobile network coverage.

Balochistan is Pakistan’s largest province and the richest in natural resources, but it is also the least developed.