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.

Terrorists in explosive vests have reportedly threatened Pakistan train passengers' lives if officials refuse to release imprisoned militants.

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.