A suicide bomber detonated an explosives-laden vehicle beside a railway track in southwest Pakistan on Sunday, killing at least 24 people and wounding more than 70 as a passenger train passed through the city of Quetta, officials said.

The force of the blast caused two carriages to overturn and catch fire, sending thick black smoke into the air. Several nearby buildings were badly damaged, and more than a dozen parked vehicles were destroyed, according to witnesses and images circulating on social media.

Doctors at local hospitals said 20 of the wounded were in critical condition.

The Baloch Liberation Army, an outlawed separatist group that demands independence from Pakistan's central government, claimed responsibility for the attack, saying it had targeted a train carrying security personnel.

Quetta is the capital of Balochistan, an oil- and mineral-rich province that has long been the scene of a low-level insurgency. Militants have frequently targeted security forces, government installations and civilians there and elsewhere in the country. At least 26 people, including soldiers, were killed in 2024 when a suicide bomber attacked a train station in the province.

The attack happened in an area where security forces are usually stationed. Three security officials told the Associated Press that bodies had been transported to hospitals following the blast, speaking on condition of anonymity.

A medical emergency was declared at hospitals in Quetta and an investigation launched, said Shahid Rind, spokesman for the Balochistan provincial government.

"We strongly condemn the targeting of innocent civilians and are deeply saddened by the loss of precious human lives," Mr Rind said. "Terrorist elements deserve no leniency."

Prime minister Shehbaz Sharif condemned the attack as a "cowardly act of terrorism" in a post on X, offering condolences to the families of the victims. Balochistan chief minister Sarfraz Bugti said the militants had targeted "innocent civilians, including women and children", vowing to pursue those responsible.

Mr Bugti and the federal government in Islamabad have repeatedly alleged that the BLA is backed by India, using the term "Fitna al-Hindustan" to refer to the group. New Delhi denies the allegation.

Pakistan and India have long had strained relations, having fought two of their three wars over the disputed territory of Kashmir, which both countries claim in its entirety.