The truce was the main objective of Petro's "total peace" policy, which aims to end the armed conflict that has persisted in the country even after the Revolutionary Armed Forces of Colombia (FARC) dissolved in 2017.

The armed groups still operating in Colombia, the world's largest cocaine producer, are locked in deadly disputes over drug trafficking revenues and other illegal businesses, according to the Institute for Development and Peace Studies (Indepaz), an independent think tank.

"We have agreed to a bilateral ceasefire with the ELN, the Second Marquetalia, the Central General Staff, the AGC and the Self-Defense Forces of the Sierra Nevada from January 1 to June 30, 2023, extendable depending on progress in the negotiations," Petro tweeted.

He said there would be a national and international verification mechanism for monitoring progress under what he called the "bold" accord.

Peace talks had been suspended under the government of Ivan Duque (2018-2022), but after Petro came to power on August 7, leading the country's first leftist government, he resumed negotiations in November.

Up to now the efforts to negotiate with Colombia's various armed groups -- with their combined total of more than 10,000 fighters -- have failed to end a spiral of violence engulfing the country. Indepaz recorded nearly 100 massacres last year.

- 50 years of conflict -

The National Liberation Army (ELN), the last recognized insurgency in the country, has been negotiating with the government since November.

On December 19 it announced a unilateral ceasefire to run until January 2. The government then called on other groups to join the truce.

The Segunda Marquetalia and Central General Staff -- splinter factions of FARC that broke from the 2016 peace pact -- have held separate exploratory talks with the government.

AGC, the country's largest drug gang, is made up of remnants of extreme right-wing paramilitaries that demobilized in the early 2000s during the presidency of Alvaro Uribe.

The government is offering the groups "benevolent treatment from the judicial point of view" for the armed actors "in exchange for a surrender of assets, a dismantling of these organizations and the possibility that they stop exercising these illicit economies", Senator Ivan Cepeda recently told AFP.

Some dissidents refused to lay down their arms alongside their FARC comrades six years ago, when the fearsome rebel army signed the deal with Bogota to end more than five decades of conflict.

Colombia has suffered more than 50 years of armed conflict between the state and various groups of left-wing guerrillas, right-wing paramilitaries and drug traffickers.

When Petro took power last August, he vowed to negotiate with all Colombian armed groups as part of his "total peace" policy.

But Uribe's right-wing Democratic Center party dismissed the "total peace" approach as "defending crime and impunity."

There are currently around 90 political and criminal groups operating in the country, according to Indepaz.