Gunmen shot dead nine Pakistani police and prison staff as they slept in Lahore on Thursday, the second attack on security forces in the country's political heartland since Islamabad reopened a NATO supply corridor.
Police said the dawn attack, in which 10 gunmen stormed a residential property housing officers from the country's troubled northwest who were in the city for training, bore the hallmarks of a similar assault on an army camp on Monday.
The killings raise fears of a fresh wave of violence in Punjab, the country's most populous province that will be vital in upcoming general elections, and which for the past year had seen a lull in attacks blamed on Taliban-linked insurgents.
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 early Thursday.
"Nine people have died so far in this attack," Rehman told reporters at the scene.
Rescue workers wrapped bodies in white sheets and survivors sobbed over the deaths of their colleagues as bullet casings lay discarded outside the two-storey grey building, television footage showed.
Lahore city police chief Aslam Tareen told AFP that nine people were also wounded.
There was no immediate claim of responsibility, but police blamed the "same gang" who killed seven security personnel at an army camp in Punjab's district of Gujrat, 150 kilometres (100 miles) southeast of Islamabad, on Monday.
"All defunct organisations are working in close cooperation with each other" to attack security forces, Rehman told reporters.
A senior security official told AFP that in Monday's attack it was "highly likely" that the gunmen belonged to a banned organisation in league with the Taliban.
Considered Pakistan's cultural capital and close to the Indian border, Lahore is a city of eight million that in 2010 suffered a string of high-profile bombings blamed on Taliban and Al-Qaeda-linked militants.
But since early 2011, it had been largely shielded from violence linked to the Islamist extremists based in Pakistan's border regions with Afghanistan in the northwest.
Tensions have been high among right-wing and extremist organisations since Pakistan last week decided to reopen its Afghan border to NATO supply convoys, ending a seven-month blockade following negotiations with US officials.
The Defence Council of Pakistan, a coalition of right-wing and hardline Islamist groups, bitterly opposes the country's alliance with Washington and the resumption of supplies for NATO troops fighting the Taliban in Afghanistan.
Hafiz Mohammad Saeed, the founder of the banned Islamist group Lashkar-e-Taiba blamed for the 2008 attacks in Mumbai, who has a $10 million US government bounty on him, has urged Pakistanis to protest.
Just hours before Monday's attack, thousands from the Defence Council of Pakistan passed through the area on a "long march" from Lahore to Islamabad to demonstrate against the reopening of NATO supply routes.
Pakistan closed the routes in protest at US air strikes in November last year that killed 24 Pakistani soldiers.
The air raid plunged ties between Islamabad and the United States, already shaky after the US raid that found and killed Osama bin Laden in a Pakistani garrison town in May 2011, to a new low.
After months of negotiations, a rapprochement was achieved when US Secretary of State apologised for the deaths in the air raid.