In the first incident of firing, two policemen were gunned down in Qayumabad area, Geo TV reported.
Hospital sources confirmed the deaths of the two police personnel.
The second incident occurred in Defence Housing society area where unknown gunmen shot dead two policemen on duty and fled the scene.
The killings of the policemen came after paramilitary rangers had earlier in the day claimed to have arrested around 400 suspects said to be involved in targeted killings, sectarian violence, arson and looting, from different areas of the city in search operations.