Ninety per cent of cocaine reaching the United States comes from Colombia - most of it via Farc rebels, a senior US official has told a magazine.
Colombia is the source of most of the world's cocaine
The Drugs Enforcement Agency's Michael Braun described the Farc as "half terrorists, half traffickers - the face of global crime in the 21st Century".
The left-wing guerrilla army is thought to be one of the world's most powerful.
Colombia's right-wing paramilitaries - players in the country's civil conflict - are also involved in the drug trade.
Under what is known as Plan Colombia, the US has given $3bn in mainly military aid to Colombia to fight the drugs trade.
In the interview with the weekly Colombian publication Semana, the DEA's chief of operations said nine out of every 10 grams of cocaine sent to the US came from Colombia, and that the majority of it had passed through the Farc at some point.
The rebel group, Mr Braun added, were making between $500m (£257m) and $1bn a year from trafficking.
However, he said, he believed the war against the Farc was being won.
Asked about the role of the paramilitary umbrella group AUC - whose members have been demobilising - in the international drugs trade, Mr Braun said he did not want to underestimate it.
But the Farc, he said, was the paradigm of the organised crime of the future because of the way it had transformed itself.
Colombia is the source of more than 70% of the world's cocaine supply, according to DEA figures.