A blast near a police car in the southwestern Pakistani city of Quetta on July 30 has killed four people and wounded more than two dozen, officials said.
Local police official Bakhat Achakzai said the attack targeted the vehicle parked in the middle of the volatile city, where security forces and members of the minority Shi'ite Muslim community often come under attack.
It was not immediately known what kind of explosive device had caused the blast, Achakzai added.
"We are still investigating if it was a suicide bombing or a device that has gone off," said another police official, Muhammad Tahir.
Four bodies -- including two children and one woman -- were taken to the city's main hospital, medical officials said.
Another 25 people were being treated in hospital and some of them were in critical condition.
There was no immediate claim of responsibility.
Balochistan is Pakistan's largest but most volatile province, which has borders with both Afghanistan and Iran and which is being targeted by Islamist militants and sectarian groups.