BOGOTA (Reuters) - A Colombian soldier held hostage for a month by the country’s rebel National Liberation Army (ELN) was freed on Thursday, the Ombudsman’s Office said, the fourth hostage released by the group in less than a week.

The release of hostages held by the ELN is President Ivan Duque’s top precondition for restarting peace talks with the group, which claimed responsibility for a bombing that killed 21 cadets at a police academy in January.

“Members of the ELN turned over first corporal Angel Mauricio Acevedo Torres, who was in the power of that armed group since January 7, to a humanitarian commission of the Ombudsman and the Catholic Church,” the ombudsman said on Twitter.

Photos shared by the office showed Acevedo speaking with ombudsman staff while standing with masked members of the ELN in front of the insurgent group’s flag.

More than a dozen more people have yet to be released, the government estimates.

Duque reactivated Interpol red notices - equivalent to international arrest warrants - for ELN leaders after the car bombing in Bogota.

Though the notoriously decentralized ELN claimed responsibility and called the attack a legitimate attack of war, its leaders, who are in Cuba, have said they were not involved.

The commanders went to Cuba in 2018 for the talks and say they will not leave unless Duque agrees to the conditions set out by his predecessor, including security guarantees in case of a breakdown in negotiations. Duque says the protocols do not apply to his new government.

The 2,000-strong guerrilla group, founded in 1964, is considered a terrorist organization by the United States and the European Union.