A Colombian oil worker was kidnapped by the country's last rebel group, the ELN, after peace talks with the government broke down and a truce expired.
Police said the man was abducted from an office in Saravena near the border with Venezuela.
The incident took place as the UN chief, Antonio Guterres, arrived in the country.
Peace talks with the ELN were suspended last week because of other attacks.
UN Secretary General Antonio Guterres was due to meet President Juan Manuel Santos and members of the UN mission in Colombia.
The talks with the ELN had been set to resume in neighbouring Ecuador, but there has been no agreement to extend the ceasefire and the government pulled out because of an ELN attack on a pipeline and a naval base.
Experts say international input from the UN is unlikely to be enough to prompt a return to the negotiating table or any changes in position.
An agreement with the ELN would end conflict in Colombia after the accord struck in November 2016 with the much larger Revolutionary Armed Forces of Colombia (Farc).
Under that deal brokered by President Santos, the Farc has disarmed and demobilized its fighters and transformed into a political party.
Who are the ELN rebels?
- The guerrilla group was founded in 1964 to fight against Colombia's unequal distribution of land and riches, inspired by the Cuban revolution of 1959
- Over the decades, the group has attacked large landholders and multinational companies, and repeatedly blown up oil pipelines
- To finance itself it has resorted to extortion, kidnappings and drug trafficking
- It has been strongest in rural areas
Mr Santos was awarded the Nobel Peace Prize in 2016 for his efforts to reach peace with the Farc.
He has spoken of his hope to also achieve a peace deal with the ELN before he leaves office later this year, but government negotiators have warned that the diffuse command structure of the ELN makes it harder to negotiate with than the Farc.