At least 80 people are dead and more than 18,000 have been forced to flee their homes in Colombia, officials say, amid fierce clashes between two rival armed groups on the border with Venezuela.

The unusually deadly violence delivers a devastating blow to the “total peace” program of the country’s first leftist president, Gustavo Petro.

At least 20 Colombian fighters from rival rebel factions were killed in weekend clashes over control of a strategic jungle area for drug trafficking, military sources and the human rights ombudsman office reported on Monday.

More than 80 people were killed following the government’s failed attempts to hold peace talks with the National Liberation Army.