At least six persons, including four police personnel, were killed on Tuesday in an explosion near the Balochistan Assembly building in Pakistan's Quetta city.

The explosion took place near a police truck parked on Zarghoon Road, in the city's high-security Red Zone, 300 metres from the provincial assembly building, Geo News reported. 

Hospital sources confirmed the death toll to Geo and said 17 others were injured in the blast.

The exact nature of the blast was not known yet, said the police. However, according to initial reports, a suicide attacker on a motorcycle was attempting to target the Balochistan Assembly building but detonated his explosives near the high-security Red Zone area. 

A large number of security personnel had been present near the site of the blast as a session of the Balochistan Assembly had just concluded. The area also houses several important government buildings.

A bus was also damaged in the blast.

Security officials said a bomb disposal team was present at the location conducting necessary search and sweep exercise.