PESHAWAR, Pakistan: Authorities found the bodies of six Pakistani men near the Afghan border Sunday who were killed by militants for allegedly spying for the US in an area that has been hit by a wave of drone missile strikes in recent weeks, said intelligence officials and residents.

The bodies of the men?-- one of whom had been decapitated?-- were found in North Waziristan, part of Pakistan's lawless tribal region that is dominated by militant groups staging cross-border attacks against US and NATO forces in Afghanistan.

One of those groups, the Haqqani network, an al-Qaida-linked Afghan Taliban faction, is considered the most dangerous threat to coalition forces and is believed to have helped orchestrate the December 30 suicide bombing at a remote base in Afghanistan that killed seven CIA employees.

The militants have responded by carrying out a wave of killings targeting people they suspect of helping facilitate the drone strikes. Pakistani intelligence officials have said at least 30 of their operatives were killed in North Waziristan in 2009, many with notes attached to the bodies alleging they were US spies.

The six bodies found Sunday had similar notes, said intelligence officials and residents.

The bodies of five men who had been fatally shot were found on the outskirts of Miran Shah, the main town in North Waziristan, said the officials, speaking on condition of anonymity because they were not authorized to talk to the media.

Authorities found the body of a sixth man who had been beheaded near Mir Ali, another town in the tribal area, said resident Razaullah Wazir.

"This is the fate of American spies," said a note attached to the body written in the local Pashtu language, according to Wazir.

The US does not discuss the CIA-operated drone strikes, but officials have said that they have killed senior al-Qaida and Taliban leaders in the country.

Pakistani officials protest the strikes as violations of the country's sovereignty, but many analysts believe the US has a secret deal with the government allowing them.