Officials and witnesses said the bomber was riding a motorbike carrying explosives and hit a military truck transporting soldiers in Quetta, capital of Baluchistan province.
The blast in a high-security zone of the city also wounded at least 32 people, said Provincial Interior Minister Sarafarz Bugti. Several of the injured were in critical condition, he added.
An army statement said an 'incendiary explosive' was used in the blast, which burned several nearby vehicles.
The deadly attack took place as Pakistan prepares to mark its independence day on Monday. Security is tightened and streets in major cities across the country during evening hours are usually crowded in the runup to the celebrations.
There were no immediate claims of responsibility. Extremists linked to the outlawed Pakistani Taliban often take credit for plotting suicide bombings and other militant attacks in the country.
Ethnic Baloch insurgents are also active in the Pakistani province and often attack security forces and government installations. Militants loyal to Islamic State have also stepped up attacks in Pakistan.