Pakistani separatists said they have taken more than 180 train passengers hostage, Tengrinews.kz reports, citing France 24. The militants have given Pakistani authorities a 48-hour ultimatum to exchange the prisoners.

"Pakistan has 48 hours to correct its mistakes," the captors said. They have captured military personnel, ISI staff members and personnel.

The Baloch Liberation Army (BLA), which is fighting for independence from Islamabad, said it took 182 hostages, including military personnel, in an attack on a train on Tuesday and threatened to kill them if security forces did not leave the area. Earlier reports put the number of hostages at 450.

A train carrying about 400 passengers was stuck in a tunnel and the driver was seriously injured, local authorities, police and railway officials said, without confirming the Balochistan Liberation Army's (BLA) claim of hostages. 

Security forces said an explosion was heard near the tunnel and they were exchanging fire with militants in the mountainous area.

The BLA, which seeks independence for Balochistan province, which borders both Afghanistan and Iran, said it killed 20 soldiers and shot down a drone. There was no confirmation from Pakistani authorities.

"The civilian passengers, in particular women, children, elderly people and Balochistan citizens, were safely released and provided safe passage. The BLA further warns that if the military intervention continues, all hostages will be executed," the militants said in a statement emailed to reporters and posted on Telegram.

The Jaffar Express was en route from Balochistan's capital Quetta to the city of Peshawar in Khyber Pakhtunkhwa province when it was hit. Pakistan's Interior Minister Mohsin Naqvi condemned the attack and said the government would not make any concessions to "beasts who shoot innocent passengers."

Spokesman Shahid Rind said the Balochistan government had imposed emergency measures to deal with the situation, without elaborating.

The BLA is the largest of several ethnic groups that have been fighting the government for decades, alleging that it had been unfairly exploiting Balochistan's rich gas and mineral resources.

The conflict has seen frequent attacks on the government, the military and Chinese interests in the region.