BOGOTA (Reuters) - Colombia’s peace deal with the former FARC rebels is at risk of failure after the arrest of a soon-to-be congressman from the now-political party on drug trafficking charges, the group said on Tuesday.

Seusis Hernandez, known by his nom de guerre Jesus Santrich, was indicted by U.S. grand jury for conspiring with three others to export 10 tonnes of cocaine, worth $320 million in street value, to the United States, Colombia’s attorney general said on Monday.

He will remain in Colombian custody until a U.S. request for extradition is formalized, the attorney general said.

Hernandez was a rebel negotiator for more than four years at peace talks between the government and the FARC, which kept its initials but renamed itself the Revolutionary Alternative Common Force when it became a political party.

The talks resulted in an accord that ended more than 52 years of fighting between the two sides and prompted more than 12,000 FARC fighters and sympathizers to hand in thousands of weapons, in what the government says is an irreversible peace process.

“With the capture of our comrade Jesus Santrich the peace process finds itself at its most critical point and threatens to be a true failure,” soon-to-be FARC Senator Ivan Marquez told journalists.

Marquez said Hernandez’s arrest is a “set-up” and called for a meeting with the United Nations Colombia mission and the government.

“This is a farce that has been put together to trick Colombian and international opinions. Extradition would be a violation of the accords, the failure of the peace process,” Marquez said.

Crimes committed by FARC members during the war are set to be adjudicated by a special tribunal, but those committed after demobilization are subject to regular judicial procedure, which includes the possibility of extradition. The government says Hernandez’s alleged crimes took place after the deal was signed.

Hernandez had been set to take up one of 10 congressional seats guaranteed to the FARC through 2026 under the terms of the deal.