A secret CIA program helped Colombia kill at least two dozen leftist FARC guerrilla leaders, AFP reports according to The Washington Post.
Washington's covert help in targeting Latin America's oldest insurgency, funded through a multibillion-dollar black budget, also includes "substantial eavesdropping help" from the National Security Agency, the newspaper said.
The secret CIA program -- separate from the $9 billion US aid package dubbed Plan Colombia, which launched in 2000 -- was initially authorized by president George W. Bush around the same time.
President Barack Obama has continued the assistance, the Post reported, citing its interviews with more than 30 current and former officials from both the United States and Colombia.
The covert program works in two ways: the US provides intelligence to help locate the FARC leaders, and it furnishes a special GPS guidance kit that helps convert standard bombs into highly-precise smart bombs.
It was thanks to US intelligence that the FARC number two, Raul Reyes, was found and killed in 2008, the report said.
The Reyes operation was carried out on March 1, 2008, in neighboring Ecuador.
"To conduct an airstrike meant a Colombian pilot flying a Colombian plane would hit the camp using a US-made bomb with a CIA-controlled brain," the Post said, adding that the United States justified the incursion in another sovereign country's territory as self-defense for Colombia.
In Bogota, Congressman Ivan Cepeda said lawmakers would ask President Juan Manuel Santos' government for an explanation "as to just what information the government has about this."
The Revolutionary Armed Forces of Colombia has conducted an insurgency against the state since its founding in 1964.
Then president Alvaro Uribe waged a fierce war against the FARC during his 2002 to 2010 presidency, reducing Colombia's largest leftist rebel group by half -- it now numbers some 8,000 fighters -- and confining it to remote areas of the country.
The FARC has been in peace talks with the government for over a year. The two sides are currently discussing drug trafficking as part of an attempt to reach a comprehensive peace deal.