“The ELN has chosen the path of war, and war they shall have,” said Petro, before declaring a localised state of “internal unrest” and “economic emergency”.
The declarations give local authorities the ability to restrict movement of people, among other measures.
Some 5000 troops are already deploying to the border area, in the hope of containing some of the worst violence Colombia has seen in years.
AFP reporters in the town of Tibú witnessed rows of heavily armed soldiers amassing in barracks and receiving orders from superior officers.
They have yet to engage guerrilla fighters directly or deploy to the most critical zones, where senior officers say violence is still raging.
Deepening crisis
Colombia has enjoyed almost a decade of relative peace, but pockets of the country are still controlled by assorted left-wing guerrillas, right-wing paramilitaries and drug cartels.
Over the weekend, terrified residents carried backpacks and belongings on overladen motorcycles and boats, or crammed on to the backs of open trucks to flee the border region.
Hundreds found refuge in Tibú, where several shelters were set up. Others crossed the border to Venezuela – for some a return to a country from where they had fled economic and political upheaval.
“As a Colombian, it is painful for me to leave my country,” Geovanny Valero, a 45-year-old farmer who fled to Venezuela, told AFP, saying he hopes the situation will be “sorted out” so he can return.
Colombia’s Defence Ministry also reported today that 20 people had been killed in fighting between rival left-wing groups in the jungle-clad Amazon department of Guaviare.
The clashes involved rival splinter groups of the Revolutionary Armed Forces of Colombia (FARC) – left-wing guerrillas who, unlike the rump FARC, have not signed peace accords.
The clashes are a serious challenge for Petro, who has backed a policy of “total peace” since he was elected in 2022.
In the face of fierce opposition, he launched negotiations with the various hardline armed groups that still control parts of Colombia.
Critics allege his conciliatory approach has emboldened groups who are deeply involved in organised crime, and allowed them space to grow in power and influence.
A 2016 peace deal with the FARC was hailed as a turning point in the six-decade-long conflict between Colombian security forces, guerrillas, right-wing paramilitaries and drug gangs, which has left nearly half a million people dead.
But dissident factions continue to control territory in several parts of Colombia, the world’s biggest cocaine producer.
– Agence France-Presse