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.

More than 80 people were killed in northeast Colombia over the weekend after the government failed to hold peace talks with the National Liberation Army.