Four personnel of the Frontier Corps (FC) were gunned down in an ambush in the city's Langovabad area early on Wednesday.
The FC security personnel were performing their routine duty along the railway track near Sariab Road.
Heavy contingent of police along with other law enforcement agencies reached the spot and kicked off an investigation into the incident.
The bodies of the deceased, whose identities are yet to be ascertained, were shifted to a nearby hospital for medical procedure.
Minister for Interior Ahsan Iqbal condemned the incident and expressed condolences with the bereaved families.
Bilawal Bhutto said that the security forces have been fighting against terrorism with bravery.
The DIG termed the firing incident in Quetta as another act of targeted killing.
Talking to media, he said that government would not spare those involved in spreading terror and fear among citizens.
Security officials inspect the attack site in southwest Pakistan's Quetta on February 14, 2018.
"Security forces have [earlier] foiled several attempts to bomb passenger trains and recovered improvised explosive devices (IEDs) planted in the same area", he added.