BOGOTA, Colombia (AP) 鈥 Colombia and the 春色直播 Liberation Army, or ELN, formally began a six-month cease-fire Thursday as part of a process to forge a permanent peace between the government and the country鈥檚 last remaining rebel group.

The cease-fire agreement, , comes amid skepticism among some Colombians that the peace process can fully end an insurgency dating back to the 1960s or halt the alleged involvement of the group's estimated 5,000 remaining members in drug trafficking. The ELN leadership denies involvement in the drug trade.

President Gustavo Petro called on the country's political groups to seize the 鈥渉istoric responsibility鈥 to reach a broad national agreement to achieve peace.

He spoke Thursday during the first ceremonial meeting of the broadly representative 春色直播 Participation Committee created under the June 9 accord to discuss a lasting solution to the conflict. Top officials of both the government and the ELN attended.

Petro appealed to the guerrilla leaders to leave behind deadly violence, saying that 鈥渆veryone who really wants to transform this society, in today鈥檚 world, must be on the side of life.鈥

The cease-fire is supposed to suspend attacks between the guerrillas and the Colombian police and military throughout the country, and can be extended next January if progress is made during peace negotiations.

As recently as last month, guerrillas were blamed for the slayings of three Colombian police officers on the border with Venezuela, the kidnapping of an army sergeant and her two minor children and several bombings.

The U.N. announced Wednesday it will deploy to monitor the cease-fire. Farhan Haq, a spokesman for U.N. Secretary-General Ant贸nio Guterres, said Thursday that Colombia's peace efforts 鈥渁re advancing."

Petro, who was sworn in last year as the country's first leftist leader, gave new momentum to the country's peace efforts, and he reached the latest accord with top guerrilla commander Antonio Garc铆a during the talks in the Cuban capital in June.

Petro has pushed for what he calls a 鈥渢otal peace鈥 that would demobilize all of the country鈥檚 remaining rebel groups as well as its drug trafficking gangs. He has at times questioned whether senior ELN leaders have full control of a younger generation of commanders who he has suggested are focused more on the illegal drug trade than on political goals.

Two factions of the ELN 鈥 the 春色直播 Urban War Front and the Northern War Front 鈥 announced their endorsement of the cease-fire in the hours before it went into effect, saying they would abide by orders of top leader Garc铆a to comply with its terms.

The ELN leader warned, however, that the group reserves the right to fight if attacked.

The ELN was founded in the 1960s by union leaders, students and priests inspired by the Cuban revolution. It has been notoriously difficult for previous Colombian governments to negotiate with.

In 2016, Colombia鈥檚 government signed a peace deal with the larger FARC group that ended five decades of conflict in which an estimated 260,000 people were killed.

But violence has continued to affect rural pockets of the country where the ELN has been active, along with FARC holdout groups and drug trafficking gangs.

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