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.

Colombia vowed "war" against left-wing guerrillas Monday, as security forces rushed to contain a wave of violence that has killed more than 100 people and threatens to derail the country's