Colombia's President Gustavo Petro speaks during a ceremony to formally begin a six-month cease-fire as part of a process to forge a permanent peace between the National Liberation Army or ELN and the government, in Bogota, Colombia, Aug 3, 2023. (PHOTO / AP)

BOGOTA - A six-month ceasefire between Colombia's government and the National Liberation Army (ELN) rebel group began on Thursday, representing the most solid progress to date for President Gustavo Petro's ambitious plans to end the country's 60-year conflict.

The ceasefire, set to run until the end of January 2024, is the product of ongoing peace talks between the ELN and the government, which restarted last year in hopes of ending the group's part in the conflict that has killed at least 450,000 people.

"Welcome to peace," Petro told the inauguration of a committee meant to ensure civil society participation in the talks.

But ELN leader Aureliano Carbonell told journalists on Thursday the group's financing activities -- which the government says include kidnapping, extortion, drug trafficking and illegal mining -- will not stop

Top ELN commander Eliecer Herlinto Chamorro - better known by his nom de guerre Antonio Garcia - ordered the suspension of offensive operations in a video on Monday but said the group would continue to defend itself during the ceasefire if needed.

The government's high peace commissioner, Danilo Rueda, had said on Tuesday the ceasefire would safeguard civilians and protect them from crimes like kidnapping.

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But ELN leader Aureliano Carbonell told journalists on Thursday the group's financing activities -- which the government says include kidnapping, extortion, drug trafficking and illegal mining -- will not stop.

"Financing activities continue," Carbonell said. "This process cannot weaken the organization."

The United Nations Secretary-General congratulated the two sides on the ceasefire in a statement on Thursday, hailing its potential to reduce civilian suffering. The UN Verification Mission in Colombia will monitor the effort under a mandate form the Security Council.

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The ELN negotiations have advanced further than any of Petro's other peace-building efforts.

The government called off a ceasefire with criminal organization the Clan del Golfo - also known as the Gaitanista Self-defense Force of Colombia (AGC) - in March over the group's alleged involvement in violent protests by informal miners.

A lawyer representing the Clan told Reuters in May the group was open to talks, but would not accept a proposal from Petro to surrender in exchange for reduced prison sentences, a potential deal that has yet to be approved by Congress.

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Last month the government announced plans for negotiations with the Estado Mayor Central (EMC) - a dissident faction of the now-demobilized Revolutionary Armed Forces of Colombia (FARC) rebels who rejected a 2016 peace agreement - but gave no date for talks to start.

Though peace commissioner Rueda in February said the government would also start talks with the Segunda Marquetalia, a FARC dissident faction that returned to arms after accusing the state of not honoring the 2016 accord, there has been no confirmation of potential negotiations.