Militants loyal to the outlawed Balochistan Liberation Army (BLA) claimed to have taken another 214 passengers hostage after attacking a train in a hilly area of the remote Bolan district of Balochistan on Tuesday, Anadolu Agency reported.
Security forces said they have got 155 hostages, including women and children, freed, while an operation for the release of the remaining passengers is underway.
Unconfirmed reports said that at least 10 passengers, including the train driver, have been killed in the ambush.
There was no official word on casualties.
According to security sources, several militants wearing explosive-laden jackets have taken positions near the hostages, compelling the troops to remain "extra careful" in carrying out the operation.
The BLA and some other groups have long been involved in attacks on security forces and citizens from other provinces.
They have been fighting for the "liberation" of Balochistan, which they contend was forcibly incorporated into Pakistan following the end of British colonial rule in united India in 1947.