According to initial reports, security sources claimed a roadside bomb exploded just as the police vehicle carrying 35 police personnel passed the Sariab Mill area on the Quetta- Sibbi Road, Dawn News reported.
However, the nature of the blast has yet to be ascertained.
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Civil Hospital Quetta Spokesperson Wasim Baig confirmed seven casualties and said that injured had been brought to the medical facility where emergency has been imposed, the report said.
Balochistan Home Minister Sarfaraz Bugti while condemning the attack confirmed the deaths in the attack. While 22 others were injured and are being treated at the hospital in Quetta.
"The war against terrorism is not over. Balochistan is on the forefront of this fight and we will not stop until there is not a single terrorist left in the area," the home minister said.
"These cowardly attacks will not hinder our security forces in executing their duties," he added.
Security forces have reached the location and cordoned off the area, and a security sweep is underway, it said.
Balochistan has experienced incidents of violence and targeted killings for over a decade. In recent months, the province has faced a number of security challenges, with security personnel in the province often being targeted in roadside explosions and suicide attacks.
Fifteen people, including eight soldiers, were killed when a suicide bomber targeted a military truck near the Pishin bus stop in Quetta on August 13.
Earlier in June, 14 people - including seven policemen - lost their lives in a suicide blast that shook Shuhada Chowk in Quetta's Gulistan Road area.