Footage appearing to show the execution-style killing of 16 policemen in the restive north-west of Pakistan has been released by the Taliban.
The video shows policemen lined up on a hillside with their hands tied behind their backs in front of gunmen who berate them and then open fire on them.
The incident is said to date from June when militants crossed the Afghan border and captured police.
Pakistan's army spokesman told the BBC the video appears to be authentic.
A note released alongside the video said that the policemen were captured during a cross-border raid from Afghanistan in June in Pakistan's volatile Dir district.
The bodies were discovered by locals once the militants had left. The BBC received mobile phone footage from a policeman in Dir showing local residents discovering the corpses.
The area is regularly targeted by insurgents and hundreds of militants were reported to have descended upon the town of Shalato in a remote corner of Dir close to the border with Afghanistan's Kunar province. At least 25 Pakistani troops were also killed during the prolonged clash. The Pakistani Taliban claimed responsibility for that attack.
The footage released by the Taliban is disturbing. The policemen are lined up on the left with only a few moments to live.
On the right, a local Pakistani Taliban commander accuses them of being the enemies of Islam and says God wants him to punish them.
Then his gunmen open fire and the men are seen collapsing as they are sprayed with bullets. Later, a militant is seen firing shots into the soldiers' heads to ensure they were all dead.
The BBC's Aleem Maqbool in Islamabad says incidents like this make Pakistan bristle with anger when it is told that it is not doing enough to fight militants. But, our correspondent adds, Pakistan's army also stands accused of abuses.
Human rights groups say there is considerable evidence that Pakistan's army has also conducted summary executions of suspected Taliban militants - an accusation the army denies.
"They are merciless terrorists and this is the threat which we are up against. We have suffered the most at the hands of al-Qaeda and its affiliates... At the same time Pakistan has delivered the most against [them]," Maj Gen Athar Abbas, Pakistan's army spokesman, told the BBC.
The army believes the attack was carried out by Pakistani Taliban fighters from Swat, who fled across the border into Afghanistan during the army's offensive there two years ago.
They have since regrouped and have been coming across the border to carry out attacks on isolated checkpoints like the one in Dir manned by the men who were killed.
Correspondents say that securing the long and porous border dividing Pakistan and Afghanistan has been a major challenge for the two countries.
Many of the militant groups that operate on either side of the border are closely linked.