With the scrutiny of nomination papers under way, the assistant commissioner is currently serving as the returning officer.
The banned Balochistan Liberation Front (BLF) has claimed responsibility for the attack.
The spokesperson for the outfit said similar strikes should be expected in the future.
According to a local official, the grenade landed in the courtyard of the office. Police constable Sabir Ali was among the 10 men to sustain injuries.
Levies personnel and security forces reached the site, and the injured were shifted to the Civil Hospital Pasni.
Some of the wounded were later moved to Karachi, which is a seven-hour drive away. The assailants managed to flee.
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