Pakistani insurgents attacked a passenger train in a tunnel and claimed to have taken over 100 hostages on Tuesday, as authorities struggled to reach the remote area. The fate of the estimated 500 people aboard was not immediately clear.

Officials said the attackers blew up the railroad track in restive southwestern Balochistan province and exchanged fire with security guards aboard the train.

The train was travelling from the provincial capital of Quetta to the northern city of Peshawar when it came under attack in Bolan district, government spokesman Shahid Rind said, calling it “an act of terrorism."

Ambulances were dispatched, but access was not easy due to the rugged, mountainous terrain, Rind said.

The separatist Baloch Liberation Army, which has waged a years-long insurgency, claimed responsibility for the attack and said it took over 100 hostages, including security forces who were on board.

Officials at Pakistan Railways said the Jafar Express train was carrying an estimated 500 passengers, including women and children.

Three security officials said the BLA, which Pakistan and the United States have designated a terrorist organisation, ambushed the train inside a tunnel and used women and children as human shields. They said troops have launched an operation to rescue the hostages.

Trains in Balochistan typically have security personnel on board. Separatists have previously carried out deadly attacks on trains in the region. In November, a separatist group carried out a suicide bombing at a train station in Quetta that killed 26 people.

Oil- and mineral-rich Balochistan is Pakistan’s largest and least populated province. It is a hub for the country’s ethnic Baloch minority, whose members say they face discrimination and exploitation by the central government. (AP)