The attack, claimed by the Tehreek-e-Taliban (also known as the Pakistan's Taliban) on Tuesday, took place on Zarghoon Road, a busy street in a high-security zone some 300 metres from the assembly of Balochistan province, of which Quetta is the capital.
Al Jazeera cited unnamed security sources as saying that the attacker, who was on foot, wanted to head towards the assembly; however, he detonated his explosives near the vehicle due to the roads being blocked.
Taliban spokesman Mohamed Khorasani described the explosion as an retaliatory attack that "Was to avenge the killing of our fighters [by security agencies] in staged encounters".
Pakistan's GEO TV cited officials of the bomb disposal team as saying that "the bomber, who was between 15 and 20 years of age, detonated between 8 and 10 kilograms of explosive material."
Pakistani Prime Minister Shahid Khaqan Abbasi strongly condemned the attack and said that acts of cowardice cannot affect the nation’s resolve in the war against terrorism.
He expressed deep regret at the loss of lives in the incident.
Abbasi offered condolences to the families of the martyred security personnel and prayed for the departed souls.
The prime minister also offered prayers for the speedy recovery of the victims injured in the terrorist attack.
Quetta, the capital of Balochistan province, has been at the centre of recent violence in Pakistan.
Balochistan has long been plagued by an insurgency by nationalist and separatist groups who seek to secure bigger shares in regional resources. The resulted chaos, coupled by lack of security, has made room for the activities of criminal gangs, human smugglers and terror outfits linked to the Taliban and al-Qaeda militant groups.
Last month, at least eight people were killed and dozen wounded in a suicide and gun attack on a church in Quetta. The attack targeted Bethel Memorial Methodist Church as worshippers gathered inside to attend a Sunday midday service.
In November, a senior police official was also killed in a similar attack, while in October at least seven police officials were killed in another roadside bombing.