"With the capture of our comrade Jesus Santrich, the peace process is now at its most critical point, faced by a genuine threat," Ivan Marquez said in a statement.

Santrich, who had been slated to take a seat in Colombia's Congress in July, was arrested on Monday in Bogota.

Colombian prosecutors said he was wanted for his alleged participation in the shipment of ten tons of cocaine to the United States, after the 2016 peace accord was signed.

President Juan Manuel Santos said Santrich could be extradited to the United States to face drug charges.

The FARC charged that his arrest was part of a plan "orchestrated by the US government with the help of Colombian prosecutors."

Santrich, who was a member of the FARC team of peace negotiators in Cuba, is a partially sighted 51-year-old, whose real name is Seusis Pausivas Hernandez.

US President Donald Trump was to have visited Colombia over the weekend, but cancelled his maiden trip to Latin America Tuesday to oversee the US response to an alleged gas attack in Syria.

"It's clear that we are facing another display of twisted US justice, as happened with Simon Trinidad," Marquez said, referring to another FARC leader who was extradited to the US in 2004 and jailed for 60 years.

Under the peace accord, repentant FARC fighters were required to confess their wartime crimes and pay reparations to victims to avoid jail. But they could still be arrested for any crimes they committed after the deal.

The landmark peace deal between the FARC and Santos's government was signed in November 2016, ending half century of conflict.

Since then, the FARC has disarmed and transformed itself into a political party, swapping its crossed-rifles emblem for a red rose. Ten of its members, including Santrich, were given seats in Congress.