The explosion also left seven people injured.

The blast occurred inside the washroom of train’s coach No. 4 and was powerful enough to blow out its iron structure, reports Dawn News.

The train, a 39UP Jaffar Express, travels from Quetta to Peshawar.

The explosion reportedly occurred when the train was on the move.

The woman killed in the incident, 55-year-old Naziran Bibi, was travelling from Sadiqabad to Okara. She had to sit on the floor beside the washroom because seats were unavailable. Ms Naziran, a resident of Nowshera, died on the spot, reports Dawn News.

Rescue officials told the newspaper that the injured people have been shifted to hospital for treatment.

“The nature of the explosive was being assessed through forensic evidence,” Rao Sardar Ali, inspector general of the Railway Police, told Dawn.

He said a team from the Counterterrorism Depart­ment (CTD) and the local police were investigating the incident with assistance from the Railway Police.

The militant group Balochistan Nationalist Army later claimed responsibility for the blast in a message published on social media.