By Jeremy McDermott BBC correspondent in Bogota

The FARC are the biggest rebel group in Colombia

They are from the leftist Revolutionary Armed Forces of Colombia (Farc) and its right-wing paramilitary rivals, United Self Defence Forces of Colombia (AUC).

Both groups are already on the US list of terrorist organisations.

Many of their leaders, who are wanted on terrorism charges by the US, may, if apprehended, now also face extradition on drugs charges.

The announcement recognises the changes in the Colombian underworld over the last five years.

The Medellin drug cartel was dismantled after the death of its notorious leader, Pablo Escobar, in 1993.

With the arrest of the Rodriguez Orejuela brothers of the Cali cartel in 1995 the drug world changed.

Militants move in

The big cartels disappeared and the drugs traffickers went underground and broke into smaller groups, or clans.

Into this vacuum moved the Farc and the paramilitary AUC.

They controlled the territory where the drug crops were grown and slowly but surely took over all stages of the drugs chain - no longer selling drugs to dealers in Colombia, but getting involved in exportation.

Between them they are now responsible for the export of much of the 800 tonnes of cocaine that leaves Colombia every year and earn up to $1bn, which funds the 40-year civil conflict.