A cease-fire between the Colombian government and the country’s largest remaining rebel group took effect on Thursday, the longest halt to hostilities the group has agreed to and a milestone in efforts to end the country’s 60-year internal conflict, which has killed roughly 450,000 people.
While the cease-fire is supposed to last six-months, it could pave the way for a permanent truce with the leftist group, the National Liberation Army, a guerrilla organization known as the E.L.N. that operates in the countryside and has helped fuel the violence that plagues parts of rural Colombia.
The agreement with the insurgent group was a top priority for President Gustavo Petro, who took office last year promising to deliver what he called “total peace’’ with all of the country’s armed groups. Mr. Petro, himself a former member of a rebel group, is the country’s first leftist president.
The cease-fire applies to combat between the E.L.N. and the state, but allows the group to defend itself if it is attacked.
Government officials hope the agreement will protect the “civilian population that has been so affected by the actions of the illegal armed organizations,” Iván Velásquez, Colombia’s defense minister, said on Wednesday.
The group’s lack of a unified command has made it difficult to negotiate with in the past. Individual factions often act autonomously — at times over the objections of high commanders.
Previous discussions between the E.L.N. and the government have collapsed several times since the Marxist-Leninist group was founded in 1964. The most recent negotiations were suspended in 2019 after the group bombed a police academy in Bogotá, the capital, an attack that killed 22 police cadets.
A newly created entity made up of the officials from the Colombian military and government, the United Nations and religious groups will monitor the enforcement of the new agreement.
The cease-fire was announced in June following three rounds of private negotiations in Cuba, Mexico and Venezuela.
“Hopefully it will bear fruit,” Mr. Petro said of the agreement in a speech on Tuesday. “It will depend more on them than on us.”
The E.L.N.’s top commander, Eliécer Herlinto Chamorro, known by his nom de guerre Antonio García, called on combatants to comply with the cease-fire in a video on Monday and said that further discussions with the “participation of society” would move forward “to make Colombia a fairer, more democratic and inclusive country.”
Colombia’s internal conflict erupted in the late 1950s as a battle between the government and a leftist insurgency group, the Revolutionary Armed Forces of Colombia, know as the FARC, but eventually grew more complex and involved other left-wing rebels, right-wing paramilitary groups and drug cartels.
The government reached a landmark peace accord with the FARC, the largest rebel group, in 2016 following an arduous five-year process.
But the E.L.N., which has around 5,800 members, according to Colombia’s defense ministry, is considered more ideological than the FARC and less hierarchical. The FARC’s disarmament left a power vacuum for other armed groups to fill, including the E.L.N., which has nearly doubled in size since 2016.
The different groups often compete for control of territory and the country’s drug trade, trapping innocent civilians in the middle.
The E.LN. has carried out kidnappings for ransom, extortion and assassinations, and is known for bombing oil pipelines and targeting government and military infrastructure. In many regions with little government presence along the Pacific Coast, as well as the border with Venezuela, they effectively act as the state.
If the cease-fire holds, it would be a major victory for Mr. Petro, who is facing a political crisis after his son was accused of laundering money from drug traffickers.
It could also potentially lead to other agreements with the E.L.N. that would specifically call for a halt in violence toward civilians, said Elizabeth Dickinson, a Colombia-based senior analyst for International Crisis Group.
“The hope is that the negotiations will have advanced far enough that we can think about other steps,” said Ms. Dickinson. “The priority for our communities and really the general population would be a cessation of hostilities.”