By ABDUL SATTAR and MUNIR AHMED

QUETTA, Pakistan (AP) — Insurgents who attacked a passenger train in Pakistan killed 21 hostages, the military said Wednesday, while security forces rescued over 300 others and killed all 50 of the assailants.

The military spokesman, Lt. Gen. Ahmad Sharif, told local media that three soldiers who had been guarding the track were also killed in the attack that began Tuesday in restive Balochistan province.

Security officials said troops rescued 346 hostages and the operation had concluded. The officials spoke on condition of anonymity because they were not authorized to speak to the media.

The province’s chief minister, Sarfraz Bugti, told a provincial assembly that troops killed all insurgents involved.

The separatist Baloch Liberation Army claimed responsibility for attacking the train carrying 440 passengers in a tunnel in a remote part of Balochistan. Spokesman Jeeyand Baloch had said the group was ready to free passengers if authorities agree to release jailed militants.

Officials did not immediately account for the remaining passengers.

The BLA regularly targets Pakistani security forces and has also attacked civilians, including Chinese nationals among the thousands working on multibillion-dollar projects in Balochistan related to the China-Pakistan Economic Corridor.

Chinese foreign ministry spokeswoman Mao Ning said her country “will continue to firmly support Pakistan in advancing its counterterrorism efforts.”

Some relatives of hostages were angry at Interior Minister Mohsin Naqvi, who last year claimed that the BLA was not a threat and “an ordinary police inspector could fix this situation.”

What happened?

The train had been traveling from Quetta to the northern city of Peshawar. Officials say the Jafer Express train was partially inside a tunnel when the militants blew up the tracks, forcing the engine and nine coaches to stop.

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

Balochistan, which borders Iran and Afghanistan, has long been the scene of insurgency. Separatists demand greater autonomy from the government in Islamabad and a larger share of the region’s natural resources.

Insurgencies on either side of the Iran-Pakistan border have frustrated both countries. Their governments suspect each other of supporting — or at least tolerating — some of the groups. Iran has sought help from Pakistan in countering the threat from the militant group Jaish al-Adl. Pakistan wants Tehran to deny sanctuaries to BLA fighters.

What did the hijackers want?

Trains in Balochistan typically have security personnel on board, as members of the military frequently use trains to travel from Quetta to other parts of the country. In November, the BLA carried out a suicide bombing at a train station in Quetta, killing 26 people.

The BLA had warned that the hostages’ lives would be at risk if the government did not negotiate.

Analysts said the attack and its focus on civilians could backfire.

“After failing to damage the Pakistan Army within Balochistan, BLA has shifted its targets from military to unarmed civilians. This may give them instant public and media attention, but it will weaken their support base within the civilian population, which is their ultimate objective,” said Syed Muhammad Ali, an Islamabad-based independent security analyst.

Rescued passengers, including women and children, were being sent to their hometowns. Some of the injured were taken to Quetta, the provincial capital, about 100 kilometers (62 miles) away.

Shams Ullah Khan said two relatives were taken hostage. Another man, Hamad Khan, said his brother was a hostage. Families were desperate for information.

Ahmed reported from Islamabad. Associated Press writers; Rasool Dawar in Peshawar, Pakistan; Ishtiaq Mahsud in Dera Ismail Khan, Pakistan; and Asim Tanveer in Multan, Pakistan, contributed to this report.