United Nations observers have been criticised after being filmed dancing with left wing guerrillas they were employed to watch over during New Year festivities in Colombia.

In footage filmed by Spanish news agency EFE during a party inside the Colombian jungle camp, two men wearing blue vests with UN insignia can be seen dancing with female guerrillas from the Marxist FARC movement.

The group has been involved in a three decade-long conflict with the Colombian government, and UN observers were recently sent into rebel camps following a peace agreement.

The scenes of merriment were celebrated by some as evidence of Colombians' determination to put aside their differences and welcome in the New Year.

Critics of the peace process though were outraged at the scenes, reported AP.

"What a joke," conservative lawmaker Maria Fernanda Cabal blasted out on Twitter. "How can we trust in the UN delegates' impartiality when they go partying with the FARC?"

The UN mission said in a statement it would investigate the incident and said the behaviour was "inappropriate and doesn't reflect the values of professionalism and impartiality of the mission."