A secret CIA programme helped Colombia kill at least two dozen FARC leaders, The Washington Post has reported.
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 on Sunday.
The secret CIA programme - separate from the $9bn US aid package dubbed Plan Colombia, which launched in 2000 - was alleged to have been initially authorised 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 the US and Colombia.
The covert programme works in two ways: the US provides intelligence to help locate the FARC leaders, and it furnishes a special satellite navigation 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.
Speaking to Al Jazeera, Robert Grenier, former counter intelligence officer at the CIA, said that he could not confirm the incidents.
But, he said that the US did not reinvent the wheel to introduce these methodologies. "These [would have been] methodologies that were introduced in Afghanistan and used here."
The Reyes operation was carried out on March 1, 2008, in neighbouring 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.
The newspaper reported that the US justified the incursion in another sovereign country's territory as self-defence for Colombia.
In Bogota, Congressman Ivan Cepeda said politicians would ask the government of President Juan Manuel Santos 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 more than a year.
The two sides are discussing drug trafficking as part of an attempt to reach a comprehensive peace deal.