With an official deadline for a final deal just a month away, peace talks between the Colombian government and the Revolutionary Armed Forces of Colombia (FARC) faced one of their most significant challenges yet this week.

Images surfaced on Thursday of some 200 armed FARC rebels apparently holding a meeting in a small town in Colombia’s northern La Guajira department alongside FARC chief negotiator alias “Iván Márquez” and other members of the guerrilla group’s peace delegation.

The government has periodically permitted FARC negotiators to travel from peace talks in Havana back to Colombia in order to meet with other FARC rebels and explain progress on negotiations. But the terms of negotiations also strictly prohibit so-called “armed politics” or using force – either real or implied – to push a political agenda, particularly one related to the ongoing talks in Cuba.

“The government considers it a fundamental rule of this accord that there will be no politics with arms,” said Colombian chief negotiator Humberto de la Calle on Thursday. “In that regard, this is an unacceptable violation.”

President Juan Manuel Santos has since banned FARC representatives in Havana from returning to Colombia until a final agreement is signed and requested that negotiators return to Cuba “as quickly as possible.”

FARC representatives vehemently denied accusations and what they called “unjustified controversy” regarding the meeting in La Guajira.

“Our spokespeople arrived from Havana with a message of peace and reconciliation to one of the departments most harshly punished by the corruption and neglect of government elites,” said the FARC in a statement Thursday.

But for critics of the peace process, the FARC’s violation of established rules is a sign that the guerrilla group may not uphold their end of the bargain when a final deal is signed.

“Why does the Santos government allow the FARC, a terrorist group, to politic with arms and in a community that has been victimized?” tweeted former President Alvaro Uribe.

Former presidential candidate and Centro Democrático leader Oscar Ivan Zuluaga offered an even harsher take on the situation.

“This constitutes an action that violates the constitution, that violates national sovereignty, challenges justice and shames the honor of our soldiers and police,” he said in a video message Thursday.

Even those more closely aligned with President Santos and the peace process in general seemed taken aback.

“The FARC error shouldn’t repeat itself but it should serve to elucidate guarantees for protection when, shortly, the reintegration into civil society begins,” wrote Clara López, leader of the Polo Democrático party, on Twitter.

Visiting La Guajira on an unrelated trip, President Santos spoke out against the FARC actions on Friday.

“What happened yesterday in La Guajira is unacceptable and goes against what we are seeking through the peace process – a definitive break in the link between arms and politics,” he said.

“ not only violated rules and protocols, but also dealt a serious blow to the confidence given them in these negotiations and the confidence of Colombians in the peace process.”

Santos also called on the FARC to wrap up as quickly as possible the remaining points of the agreement to be reached in Havana and asserted that the protection of Colombian civilians would always be the top priority.

“We have already discussed this sufficiently,” he said. “The Colombian people want and demand reassurances that will recuperate confidence in the process.”