The death toll from a militant hijacking of a train in Pakistan's southwestern mountains has risen to 31 soldiers, staff and civilians, the military said on Friday as it accused India and Afghanistan of backing the insurgents.

A group of militants seized a Peshawar-bound train, igniting a 36-hour hostage crisis, but this attack is part of a decades-long insurgency rooted in the Baloch separatist groups' violent struggle for an independent state.

The train hijacking in south-western Pakistan represents a major escalation in the region’s long-running insurgency.

Nearly 200 have been freed but the status of other passengers remains unclear as security forces continue to battle separatist militants.

"Terrorists were in direct communications with Afghanistan-based planners throughout the incident," he said. The Foreign Office statement came after the army also officially confirmed the Afghan link to the brazen train hijacking.

In the clearance operation that lasted more than 30 hours, the Pakistan military said it killed 33 BLA terrorists. Chaudhry, director general of military public relations, said 354 passengers were freed, 37 of whom were injured. Officials also revised the tally of passengers on the train downward to 425 from 440.

The Baloch Liberation Army (BLA) claimed responsibility for the execution of 214 hostages after Pakistan refused to negotiate a prisoner exchange. The mass execution included only Pakistan security personnel,

The BLA said they gave the Pakistan Army 48 hours to exchange prisoners of war, but since they did not heed their warning, they killed the hostages