The bomber struck as workers of the PML-Q party, which is part of the ruling coalition at the centre, were preparing for a rally to be addressed by senior party leader and former federal minister Amir Muqam.
Witnesses said the bomber blew himself up near a group of policemen deployed to guard the rally. The blast hit an office of the water and power utility located near the venue of the rally, witnesses told the media.
Police officials said at least six persons, including three policemen, were killed in the attack. The injured were taken to nearby hospitals.
PML-Q workers said senior leader Amir Muqam was safe as he was not at the venue at the time of the blast. No group claimed responsibility for the attack though such suicide bombings are usually blamed on the Pakistani Taliban.