BOGOTA (Reuters) - Colombia's government on Wednesday asked a United Nations mission tasked with supervising the demobilization of Marxist FARC rebels to safeguard its neutrality, after the publication of a video showing UN staff dancing with rebels at a New Year celebration.

Rebels from the Revolutionary Armed Forces of Colombia (FARC) are beginning a demobilization process that will end more than five decades of war after signing a peace deal with the government of President Juan Manuel Santos.

The UN mission will take possession of all FARC weapons and run more than two dozen demobilization camps.

In a public letter, Maria Emma Mejia, Colombia's ambassador to the UN, said the conduct shown in the video of the holiday celebration, published by local and international media this week, was a source of "great worry and surprise."

"This type of behavior distorts the professionalism and neutrality that should characterize, at all times, the team that is part of the tripartite mechanism for the monitoring and verification of the ceasefire and definitive laying down of arms," the letter said.

The UN should ensure the incident is not repeated, the letter added, in order not to put at risk public confidence in the multinational organization.

The UN has said the actions of the staff shown in the video, which sparked social media condemnation from right-wing opponents of the peace deal, were inappropriate and that it will take measures to avoid putting its professionalism in doubt.

The FARC has said the reaction to the video is overblown.

"Let's leave behind the hatred and get in step with peace and reconciliation," FARC leader Rodrigo Londono, better known as Timochenko, tweeted on Wednesday, adding the hashtag "I dance for peace."

The UN currently has 280 observers working as part of the demobilization mission.

(Reporting by Luis Jaime Acosta and Julia Symmes Cobb; Editing by Leslie Adler)