QUETTA, Pakistan — Two bombs struck a passenger train minutes apart in southwest Pakistan on Friday, killing at least six people and wounding 19, officials said.

The first bomb exploded on the train and the second device, which was planted on the railway track, struck the moving train near the village of Mach in Baluchistan province, according to railways official Tufail Ahmad and local police official Mohammad Sajid.

Ahmad said the train was heading to the garrison city of Rawalpindi in the eastern province of Punjab from Quetta, the provincial capital of Baluchistan, at the time. He said the casualties were taken to nearby hospitals and that some of the wounded were in critical condition.

Initially officials said only one bomb went off and three people were reported dead, but three more later died of their injuries, according to Sajid, who examined the damaged train and track.

No one immediately claimed responsibility for the attack, but separatist groups in the province have claimed similar attacks in the past.

Baluchistan has long been the center of a low-level insurgency by nationalist groups that demand more autonomy and a greater share in the region’s natural resources. The government says it’s trying to improve people’s welfare in the province and bring the separatists into mainstream politics.

Railways Minister Khawaja Saad Rafique denounced the bombing as “an act of terrorism” and said authorities were still trying to determine how the bomb was planted on the train.

Prime Minister Nawaz Sharif condemned the attack and ordered authorities to find and arrest those behind it.