The foreign ministry has rejected criticism by Colombia over the role played by a Swiss mediator involved in negotiations with rebel group Farc.

Colombian authorities have accused Jean-Pierre Gontard of transporting ransom money for the leftwing group during the release of two hostages in 2001.

"We have no evidence at all that he went beyond his mediator mandate," said Deputy State Secretary Anton Thalmann in an interview with the NZZ am Sonntag newspaper - the first comments by a high-ranking official.

Colombian authorities maintain Gontard transported money for Farc during a mission to negotiate the release of two Novartis employees held by the group.

They point to documents reportedly found on the computer of the former Farc number two, who was killed by the Colombian army on March 1 in Ecuador.

Thalmann reiterated that Gontard would continue to work for the foreign ministry after a "helpful and successful" ten years mediation.

It has also emerged that Colombian politician Ingrid Betancourt, who was held hostage for six years by Farc rebels, has personally called Swiss Foreign Minister Micheline Calmy-Rey to thank her for Switzerland's hostage negotiation efforts.

Betancourt was released earlier this month after an audacious rescue operation.

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