President George W Bush personally "leaned on" director of the CIA George Tenet to co-operate with Colombian forces as they sought and killed Leftist rebels in the 2000s.
According to the Washington Post, the CIA provided troops loyal to President Uribe with smart bombs and surveillance which were used to kill at least two dozen rebel leaders.
Until US intervention Farc - Revolutionary Armed Forces of Colombia - was one of the deadliest movements in the world, kidnapping and murdering as part of a decades-old war against the state.
Those suspected of sympathising with Farc - including academics and students - were also kidnapped and killed; Colombia had the highest murder rate in the world.
Then, on 13 February 2003, a light aircraft carrying a high-ranking Colombian officer and four US contractors crash-landed in dense jiungle. Farc rebels killed the officer and one of the men and kidnapped the other three.
Having decided after 9/11 there could be no hiding place for terrorists anywhere in the world, Bush allegedly asked the CIA to find the hostages.
The CIA began supplying surveillance equipment and smart-bombs used in Iraq. Once the US had negotiated a tricky legal minefield, the bombs were used by the Colombians to kill Farc leaders including Raul Reyes hiding out in the jungle across the border in Ecuador, which triggered a serious diplomatic incident.
The CIA also showed the Colombians how to interrogate captured Farc rebels, providing them with jobs and money rather than simply using torture to obtain information.
On 2 July 2008, the three American hostages were finally released unharmed. Farc has declined in influence and number ever since, but the latest revelations about US involvement in Colombia's internal affairs continue to cause controversy.
The CIA has declined to comment on the latest reports, though in Colombia president Juan Santos said the agency had helped provide forces with "better training and knowledge".