Masked gunmen have shot dead nine policemen and prison staff in an attack on a building in Pakistan's eastern city of Lahore, in the Punjab.
The Pakistani Taliban have claimed responsibility for the shootings, which wounded nine others and took place as the police were sleeping.
The gunmen arrived on motorbikes before storming the building, which is in a densely populated area.
The attack has raised fears of a new wave of violence in Pakistan, which is battling an internal insurgency from a number of militant groups, including the Pakistan Taliban.
It is the second incident in Pakistan’s Punjab province in the last couple of days.
On Monday, gunmen – using similar tactics – shot dead seven security personnel at an army camp about 100 miles southeast of the capital, Islamabad.
This assault though is particularly shocking as Lahore is part of the country’s political heartland and is well away from the troubled tribal areas in the North West.
The city’s police chief, Aslam Tareen, told the AFP news agency: "The gunmen came early in the morning, entered the building and opened fire."
Analysts believe these new attacks are likely to have been committed by a militant group in league with the Pakistan Taliban.
Extremist organisations have vowed to launch multiple strikes against security targets in retaliation for a softening of the Pakistani government’s position to Nato and the United States.
The country last week announced it would re-open vital routes used by the coalition to take supplies into Afghanistan.
The blockade was put in place after US jets blasted Pakistani military positions in November, killing 24 soldiers.
The incident – put down to a misunderstanding - caused a major diplomatic spat between Washington and Islamabad.
The supply routes were only re-opened after the US Secretary of State, Hillary Clinton, made a carefully worded apology to her Pakistani counterpart.
It came seven months after the air strikes. But the move has angered large swathes of the population.
The Defence Council of Pakistan – a coalition of right wing and Islamist groups – has already staged a number of hysterical demonstrations attacking the decision to resume supplies.
One of its members, Hafiz Saeed – who founded the banned terror group Lashkar-e-Taiba, which is blamed for the 2008 Mumbai attacks – is urging all Pakistanis to rise up in protest.