BOGOTA, Colombia — An employee of the United Nations has been kidnapped by a dissident rebel faction in southern Colombia, marring a visit by the UN Security Council Thursday to show support for the South American nation’s recent peace deal.

President Juan Manuel Santos’s administration said that the Colombian national was working on a crop substitution project in the southern state of Guaviare when he was taken captive late Wednesday. Rodrigo Pardo, the president’s top aide for post-conflict planning, said the captors are members of a unit of the Revolutionary Armed Forces of Colombia who refused to lay down their weapons as part of a peace deal last year.

‘‘These people live thanks to drugs, and they want to continue living that way,’’ Pardo said, adding that the incident wouldn’t stop the government in its goal of eradicating cocaine crops in areas once dominated by the group.

A group of UN officials were attempting to negotiate the worker’s release.

‘‘Obviously the situation when someone’s been kidnapped, the less we say the better,’’ UN spokesman Stephane Dujarric said. ‘‘What I will tell you is that we’re obviously in touch with the Colombian authorities to help secure the person’s release.’’

Santos met Thursday with ambassadors to the UN Security Council who are in the country to demonstrate their commitment to ending a half-century war that has caused more than 220,000 deaths and displaced nearly 6 million people.

Associated Press