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, declaring a state of emergency and deploying thousands of soldiers to contain a wave of violence.

Colombia vowed "war" against left-wing guerrillas Monday, declaring a state of emergency and deploying thousands of soldiers to contain violence that killed at least 100 people and threatens to scupper the country's fragile peace process.

More than 80 people were killed in the country’s northeast over the weekend following the government’s failed attempts to hold peace talks with the National Liberation Army, a Colombian official said.

Colombian President Gustavo Petro suspended peace talks with the leftist National Liberation Army (ELN) on Friday, after accusing the group of committing a war crime in the Catatumbo region, in the country's Norte de Santander province.

The ELN, which has an estimated 6,000 fighters, reportedly attacked civilians it accused of collaborating with a rival group, the FARC-EMC, shooting them in the streets, while in rural areas firefights broke out between members of both groups.

More than 8,000 civilians fled the violence, with many seeking shelter in government facilities or hiding in the mountains.