The man's remains were found late Tuesday in a sack by the side of a road in Jandola, a town in the troubled South Waziristan tribal region, in the fifth such killing in Pakistan this year, the officials said.

A note in Urdu was pinned to the bag identifying the man as Akhtar Usman, an Afghan, and saying his death "is a result of spying for Americans" across the border in Afghanistan, the officials said.

The militants also scrawled the word "hypocrite" across his forehead, they said.

Pro-Taliban militant sources said Usman was an Afghan who taught at a religious school, or madrassa, in Miranshah, the main town in neighbouring North Waziristan region.

"He had been speaking against Taliban and had recorded several audio cassettes against militants," a militant source told AFP, but declined to identify the killers.