Four people were martyred and 20 injured on Sunday in a suicide attack near a Frontier Corps (FC) checkpost on Mastung Road in Quetta, Deputy Inspector General of Quetta police Azhar Akram confirmed.
He said that 18 of the injured were security officials while two were bystanders, adding that the number of casualties could rise.
A suicide bomber on a motorcycle packed with six kilogrammes of explosives rammed one of the vehicles in an FC convoy, Akram was quoted as saying by Reuters.
The banned Tehreek-i-Taliban Pakistan (TTP) claimed responsibility for the attack.
Prime Minister Imran Khan condemned the attack, saying in a tweet: "My condolences go to the families of the martyrs & prayers for the recovery of the injured. Salute our security forces & their sacrifices to keep us safe by thwarting foreign-backed terrorists' designs."
Opposition leader and PML-N President Shehbaz Sharif said he was "grieved to learn about the martyrdom of 3 FC personnel" in the attack.
"I pay my homage to our armed forces for their sacrifices in defending the motherland. My heartfelt condolences go to bereaved families & prayers for early recovery of the injured," he tweeted.
Condemning the attack and offering condolences to the families of those martyred, Minister for Human Rights Shireen Mazari said the "brave security forces continue to thwart the designs of terrorists [especially] the RAW- (Indian intelligence agency) funded TTP."
Balochistan Home Minister Mir Ziaullah Langove too strongly condemned the attack and asked authorities to submit a report in this regard.
"Security forces have given countless sacrifices in the war against terrorism," he said, adding that the war would continue until total peace was achieved.
"The whole nation is indebted to the martyrs. We are fighting the terrorists with our full strength and will continue to do so. These violent attacks will not lower the morale of the forces," he stressed.
The attack comes less than two weeks after three Levies personnel were martyred and as many injured when their vehicle hit a landmine in the province's Ziarat district.
Earlier that week, a Pakistan Army captain was martyred and two soldiers injured when their vehicle hit an improvised explosive device (IED) planted by terrorists in the Gichik area.
There has been an uptick in violence in the province, with several incidents of terrorism reported this year, targeting both civilians as well as security forces.