Anwar Saeed’s life was at risk either way, whether fighting with the Taliban and Al Qaeda in Pakistan’s restive tribal region or spying on them for U.S. forces in Afghanistan.

But he chose the second option. The promise of $6,000 from U.S. intelligence agents was enough for him to buy better health services for his aging parents, and perhaps a chance to be self-employed in some big city, where he could vanish with his family and be anonymous among millions of people.

The gamble did not pay off. Saeed, 21, was caught before he could guide a Hellfire missile fired from a U.S. pilotless aircraft to the hideouts of two important Taliban commanders in the Khaisor and Sholam areas of South Waziristan.

"He was one of us but some of his moves made him a suspect," said a local Taliban fighter, who requested to be identified only by his alias Mohammed Zia. "We took him to our headquarters, seized his Kalashnikov, and showed him the knives we wanted to use to cut his throat, and he told us everything."

According to Zia, the "traitor" had planted two microchips that identified the places for U.S. drones in two different villages where two Taliban commanders were supposed to be on a night in October.

There is no mercy for U.S. spies in South Waziristan, a stronghold of Pakistani Taliban chief Baitullah Mehsud, whose more than 20,000 fighters launch regular cross-border attacks on international troops in Afghanistan.

After hours of torture, spies are beheaded with a sharp knife, or shot dead. Their bodies are dumped in a public place with the severed head and a note saying: "All those spying for the U.S. will meet the same fate."

Such executions are becoming more common as the U.S. has recently put in more efforts to recruit informants in South Waziristan and its neighbouring district of North Waziristan.

Most of the informants are recruited from among the tribesmen who live on the Afghan side of the border, but frequently visit relatives in the Pakistani tribal region.

"These Afghans either carry out an assigned task by themselves or share a portion of their promised reward with a local to accomplish the job," said a Pakistani intelligence official, who conceded that his colleagues were also sharing "some information" with U.S. forces.

With the help of an expanded intelligence network, the U.S. military have carried out about three dozen drone attacks since August. Many of these proved to be successful in eliminating second-rate Al Qaeda operatives and Taliban leaders.

The spies are given small equipment, containing a small transmitter and a battery that lasts for about 48 hours. The instrument is placed inside or outside the house of a militant, or planted on his vehicle.

The transmitter sends signals to a U.S. satellite, which conveys it to U.S. forces operating in Afghanistan or directly to a drone awaiting the target co-ordinates to strike.

"The accuracy of the guided missile is just a few feet, probably three to four. It can pick up a single specified target situated in a cluster of buildings, without damaging the adjacent compounds," said Syed Shah Mehmood.

He is the general manager of East West Infiniti, a company that manufactures Unmanned Aerial Vehicles for the Pakistani military.

But each successful air strike against the Islamist insurgents is followed by one or two beheadings.

Last week, the Taliban released a video of five men, including Pakistani soldiers, accused of providing "secret information" about the whereabouts of Al Qaeda leader Abu Laith al-Libi, leading to a U.S. missile strike that killed him and 11 others in North Waziristan.

The Pakistani intelligence official, who spoke on condition of anonymity, said over the past two years about 150 suspected U.S. spies have been executed.

Well aware of his fate, Saeed decided not to allow the Taliban to make an example out of him.

"We were on our way back to the headquarters after recovering the chip from Sholam," the Taliban fighter named Zia recounted. "I . . . saw him (Saeed) punching on a small instrument that looked half a size of a cellphone.

"A few minutes later our vehicle was hit by a missile. Four of my colleagues and Saeed died, and I survived miraculously with minor injuries," Zia said.