Islamabad: More than 340 train passengers taken hostage by a militant group were freed on Wednesday by security forces after a 30-hour siege, an army official told AFP, confirming that 27 off-duty soldiers were shot by militants. Pakistan security forces launched a rescue mission on Tuesday afternoon after a separatist group bombed a railway track in mountainous southwest Balochistan and stormed a train with around 450 passengers on board.

"346 hostages were freed and over 30 terrorists were killed during the operation," an army official told AFP on condition of anonymity because he was not authorised to speak to the media.

The 27 slain soldiers had been travelling on the train as passengers, the army official said. One on-duty soldier was killed in the clearance operation.

The official did not give a civilian death toll, but earlier a railway official and paramedic said the train driver and a police officer had been killed.

The assault was immediately claimed by the Baloch Liberation Army (BLA), which released a video of an explosion on the track followed by dozens of militants emerging from hiding places in the mountains.

Attacks by separatist groups who accuse outsiders of plundering natural resources in Balochistan, which borders Afghanistan and Iran, have soared in the past few years, mostly targeting security forces and ethnic groups from outside the province.

In a statement released after claiming the assault, the BLA demanded an exchange with security forces for its imprisoned members.

Passengers who escaped or were released by the militants described panic as gunmen seized control of the train, sorting through identity cards, shooting soldiers but freeing some families.

"They asked us to come out of the train one by one. They separated women and asked them to leave. They also spared elders," said Muhammad Naveed, who managed to escape.

"They asked us to come outside, saying we will not be harmed. When around 185 people came outside, they chose people and shot them down," he added.

The BLA has staged a series of recent attacks against security forces and ethnic groups from outside the province who they accuse of benefiting from the region's wealth. The group has demanded an exchange with security forces for its imprisoned members.

Several passengers told AFP that gunmen demanded to see identity cards to confirm who was from outside the province, similar to a spate of recent attacks carried out by the BLA.