By Barbara Plett
BBC News, lslamabad
Pro-Taleban militants in Pakistan's tribal areas have released a video of 16 kidnapped soldiers.
The footage shows one of them being beheaded.
The abductions coincided with a sharp rise in violence over the past month as peace deals between the government and the tribesmen unravelled.
More than 60 soldiers and 250 militants have died in a growing insurgency in the border regions near Afghanistan as troops have redeployed heavily.
The video shows four armed teenagers standing behind a soldier before one of them cuts off his head.
North Waziristan is a haven for anti-government militants
The footage was released amid negotiations to free the 15 soldiers still held by militants in the tribal area of South Waziristan.
Crucially, elders are trying to restore a peace deal that has been severely strained by the recent redeployment of troops.
The return of military check posts also triggered the end of a peace agreement in neighbouring North Waziristan.
Since mid July, pro-Taleban tribesmen there have carried out almost daily bombings against the Pakistan army.
The military said it has boosted its presence in the tribal areas to stem a wave of attacks spreading throughout the country.
But it is widely believed it also acted under strong American pressure to resume operations in the border region.
US officials say that a peace deal struck in the past two years failed to stop the flow of Taleban and al-Qaeda fighters into Afghanistan, creating a sanctuary for them instead.
The Americans have threatened to take action if Pakistan does not.
At the weekend, coalition forces admitted to another strike across the border, although Pakistan denied it took place.
The growing insurgency in the tribal area has alarmed Pakistanis.
Analysts agree that pro-Taleban forces largely control the region but they also say military force alone only strengthens support for the militants.