Colombia's leftist President Gustavo Petro restarted peace talks with the National Liberation Army (ELN) last year, but those negotiations were thrown into disarray in March, after the ELN killed nine Colombian soldiers near the border with Venezuela.

Any ceasefire must be "achievable and measurable" to win over the Colombian public, ELN chief negotiator Pablo Beltran told reporters shortly after arriving in Havana for a third round of talks since Petro's election.

"We want ... the Colombian people to see a ceasefire is possible, and that we have agreed to comply," Beltran said. "This (would be) a preliminary ceasefire, not an end to the conflict, so we are interested in it working 100%, that is, zero errors."

Beltran said the March attack that killed nine soldiers was brought on by an "offensive campaign" by Colombia's military.

"There was a series of attacks. What was our response? To defend ourselves. That was the directive," Beltran said.

The attack by the ELN, Petro's government said, damaged Colombian's confidence in the group's commitment to peace. But Beltran said the Colombian military had also killed its fighters in combat operations since the talks began.

"For now, there is no ceasefire. And operations on both sides continue," Beltran said, reaffirming his group's desire to reach a ceasefire during the Havana talks.

Negotiations with the ELN under previous administrations faltered after dissent flared from within its ranks, but Beltran rejected that would be a problem this time around, saying any such agreement would be abided by all of the ELN´s fronts.

Petro's government and the ELN concluded a first round of peace talks in Caracas at the end of 2022. A second round of peace talks were held in Mexico this year.

The ELN, founded in 1964 by radical Catholic priests, has some 5,850 members, including 2,900 combatants, and is accused of financing itself through drug trafficking, illegal mining and kidnapping.

(Reporting by Dave Sherwood in Havana; Additional reporting by Luis Jaime Acosta and Oliver Griffin in Bogota; Editing by Stephen Coates)

By Dave Sherwood