The killings took place on Thursday evening in North Waziristan, a lawless Al-Qaeda and Taleban sanctuary on the Afghan border where the United States has stepped up attacks with missile-firing drone aircraft, fueling militant fears of spies.
Five masked militants paraded the hand-cuffed men before dozens of people in the Datta Kheil area and accused them of passing information to the United States on targets for its CIA-operated pilotless drone aircraft.
"They strapped explosives around their bodies and then blew them up," a Pakistani intelligence official in the region told Reuters by telephone.
Militants have killed hundreds of people they suspect are spies for the United States or the Pakistani government over the past few years.
They usually decapitate or shoot the suspects. Residents said this was the first time the militants had blown up suspected spies.
Pakistan's northwestern ethnic Pashtun tribal lands along the Afghan border have never been under the full control of any government and have for decades been Islamist militant hubs.
During the 1980s, the tribal belt was a staging area for the US- and Pakistani-backed jihad, or Muslim holy war, against Soviet forces occupying Afghanistan.
Many Taleban and Al-Qaeda fighters fled there after US-led forces ousted the Taleban from Afghanistan in the weeks after the Sept. 11, 2001, attacks on the United States.
A separate Pakistani Taleban force then emerged from the Pashtun tribes and they have been waging war against the Pakistani state in recent years.
The army launched a major offensive in the Pakistani Taleban bastion of South Waziristan last October, killing hundreds of insurgents and destroying their main bases. Many militants took refuge in North Waziristan, officials said.
The United States wants Pakistan to extend its offensive to North Waziristan and go after militants there, particularly Afghan Taleban, who launch cross-border attacks on Western forces in Afghanistan.
The Pakistani military, which has long seen the Afghan Taleban as tools for limiting the influence of old rival India in Afghanistan, says it will deal with North Waziristan but in its own time.
