Nine Pakistani police and prison staff were killed in dawn attacks when 10 gunmen stormed a building in Lahore.
Punjab police chief Habibur Rehman said the attackers came on three motorcycles and one car, armed with Kalashnikov rifles and hand grenades.
They then stormed the building in the densely populated area of Ichra, where up to 35 police and prison staff were sleeping.
The officers from the country's troubled northwest were in the city for training.
The Pakistani Taliban claimed responsibility for the dawn raid.
The killings raise fears of a fresh wave of violence in Punjab.
Punjab is the country's most populous province and will be vital in upcoming general elections.