"It's not a ceasefire for the end of the conflict, it is a preliminary ceasefire. We're very interested in it working," Pablo Beltran told a news conference on the eve of the third round of negotiations in Havana, set to open in the Cuban capital Tuesday.

"In a conflict as complex as the Colombian one, where there are multiple (armed) groups and where there is a very high level of distrust, we must be very cautious so that what is specified is achievable, because otherwise it will lead to more distrust," Beltran said.

Negotiations nearly fell through after an ELN attack last month that killed nine soldiers, but Beltran said the group was committed to the talks.

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

Fighting has continued despite a breakthrough peace deal that saw the massive FARC guerrilla group disarm in 2017.

The government resumed peace talks with the left-wing ELN, considered the last active guerilla group in Colombia, after President Gustavo Petro took office last August pledging to bring a "total peace" to the country.

"We feel like partners of the government," Beltran said, saying that with Colombia's first left-wing government in charge, "it is possible to move forward."

He added that it was important for society to weigh in not just on how to stop the violence, but also on the social and economic problems that the ELN views as the root of the conflict.

The 3,500-strong ELN has taken part in failed negotiations with Colombia's last five presidents.