Militants in Pakistan have taken 35 passengers hostage after attacking a train in the south-western province of Balochistan. About 350 other passengers are believed to be safe, police said on Tuesday.
The Baloch Liberation Army, a separatist militant group, said it had 182 hostages and threatened to kill them if security forces did not leave the area.
The train was trapped in a tunnel and the driver was badly injured, authorities, police and railway officials said.
"Around 350 passengers, including women and children, are safe and a relief train will be reaching the area where the train was attacked," said senior district police officer, Rana Dilawar. "Security forces launched a massive operation." He said helicopters and special forces had been sent to the scene.
Security forces said an explosion had been heard near the tunnel and that they were exchanging fire with the militants in a mountainous area.
The BLA, which seeks independence for the Balochistan province which borders Afghanistan and Iran, said it had killed 20 soldiers and shot down a drone. There was no confirmation of that from Pakistani authorities.
The group said the hostages included members of the Pakistan army and other security officials who were travelling on leave.
"Civilian passengers, particularly women, children, the elderly, and Baloch citizens have been released safely and given a secure route," it said in a statement emailed to journalists and posted on Telegram. "The BLA further warns that if military intervention continues, all hostages will be executed."
The Jaffar Express was travelling from Balochistan's capital Quetta to the city of Peshawar in Khyber Pakhtunkhwa province when it was attacked.
Pakistan's Interior Minister Mohsin Naqvi said the government would not make any concessions to "beasts who fire on innocent passengers".
The Balochistan government has imposed emergency measures to deal with the situation, spokesman Shahid Rind said, without giving more details.
The BLA is the biggest of several ethnic groups battling Pakistan's government for decades, saying it unfairly exploits Balochistan's rich gas and mineral resources.
The conflict has been marked by frequent attacks against the government, army and Chinese interests in the region.
