Colombian authorities arrested a former top rebel peace negotiator on a U.S. drug warrant Monday, delivering a major blow to the country’s teetering attempts to put a half-century of political violence behind it.

Seuxis Hernández, a blind rebel ideologue best known by his alias Jesús Santrich, was picked up at his residence in Bogota on charges that he conspired with three others to smuggle several tons of cocaine into the United States with a wholesale value of $15 million.

According to an Interpol notice, Santrich met with cocaine buyers at his residence on Nov. 2, a day after one of his co-conspirators delivered a five-kilogram sample of the narcotic to them at a hotel lobby in Bogota. During the meeting and subsequent negotiations, he and his co-conspirators allegedly discussed plans for a 10-ton drug shipment to the United States, boasting they had access to cocaine laboratories and U.S.-registered planes to produce and move the drugs inside Colombia, the world’s largest producer of the illegal narcotic.

President Juan Manuel Santos confirmed the arrest in a nationally televised address, saying his “hand won’t shake” in signing off on Santrich’s extradition to safeguard the peace agreement’s integrity.

Under terms of the accord with the Revolutionary Armed Forces of Colombia, or FARC, rebels who lay down their weapons and confess their war crimes to special peace tribunals are to be spared jail time and extradition. However, they are not protected for crimes committed after the December 2016 signing.

“The construction of peace requires the absolute commitment and respect for the law and the accords,” Santos said. “This is what the Colombian people demand. In this aspect, there can’t be any room for tolerance or weakness.”

Santrich’s former comrades in arms accused the government of trying to sabotage the peace process. “This is the worst moment that the peace process has gone through,” said the former rebel leader known as Iván Márquez, who served as chief negotiator during the peace talks.

But Chief Prosecutor Néstor Martínez said a New York grand jury handed up an indictment after evaluating evidence, including videos and communications, that indicated Santrich and the three others who were arrested hatched a plan in the second half of 2017 to smuggle into the United States cocaine with a street value of $320 million.

The FARC’s ties to Colombia’s flourishing drug underworld have always been a sore spot for the rebels. The FARC long funded itself by leveling a “war tax” on cocaine moving through territory it dominated, and 50 members of its leadership structure — though not Santrich — were indicted in 2006 in the United States on charges of running the world’s largest drug cartel.

But the FARC always denied direct involvement in the business itself, and rebel peace negotiators in 2013 denounced drug trafficking as a “scourge” that has “contaminated” the international financial system and generated a global health crisis.

Santrich, 51, was one of the first rebels to bet on peace, traveling to Norway’s capital in 2012 to kick off negotiations with Colombia’s government and then participating in talks that continued the next four years in Cuba, where he earned a reputation as being a hard-liner.