More than 70 US military advisers, mostly special forces personnel, are secretly working in Pakistan to help its armed forces battle Al-Qaeda and the Taliban in the country's lawless tribal areas.
The Americans are mostly Army Special Forces soldiers who are training Pakistani Army and paramilitary troops, providing them with intelligence and advising on combat tactics, military officials told the New York Times.
But they do not conduct combat operations, the officials added.
They, the paper said, make up a secret task force, overseen by the United States Central Command and Special Operations Command.
It started last summer, with the support of Pakistan's government and military, in an effort to root out al-Qaeda and Taliban operations that threaten American troops in Afghanistan and are increasingly destabilizing Pakistan, the Times said.
It is a much larger and more ambitious effort than either country has acknowledged.
Pakistani officials, the paper noted, have vigorously protested American missile strikes in the tribal areas as a violation of sovereignty and have resisted efforts by Washington to put more troops on Pakistani soil.