The blast on Wednesday was the third in a month to hit the line from Quetta, the capital of Pakistan's Baluchistan province, to Zahidan in neighbouring Iran.

A scheduled fortnightly train between the two cities left early Thursday after engineers worked overnight to repair the track, Pakistan Railways Chief Controller Mohammad Shoaib told AFP.

"Terrorists hit the line at Naushki, some 150 kilometers (94 miles) west of Quetta on Wednesday," he said.

Impoverished Baluchistan is in the grip of an escalating rebellion by nationalist tribesmen demanding jobs and more royalties for the natural resources extracted from their region.

Thousands of troops moved into the area in January after the rebels rocketed Pakistan's biggest gas field at Sui in Baluchistan in retaliation for the rape of a woman doctor at the facility, killing eight people.