PARIS, March 6 (Reuters) - French President Nicolas Sarkozy warned the leader of Colombia's FARC rebel movement on Thursday that he would be viewed as murderer throughout the world if he let hostage Ingrid Betancourt die.

Fears for Betancourt's safety rose this week after Colombian forces announced they had killed a FARC rebel commander who was the contact person for Paris in hostage negotiations.

In an interview published in Le Figaro daily, Sarkozy said he had taped an appeal to be shown on Colombian television urging the release of Betancourt -- a French-Colombian national who was seized by rebels six years ago.

"I want to tell the FARC, continue in your strategy of humanitarian releases. Don't do something that can't be undone. Ingrid is in danger of dying," he was quoted as saying.

He said the aging leader of the Revolutionary Armed Forces of Colombia (FARC), Pedro Antonio Marin, also known as "Manuel Marulanda", could determine Betancourt's fate.

"It is up to him to know how he wants to be seen by the whole world, either as a murderer or as someone who has the courage to make a humanitarian gesture," Sarkozy said.

A group of FARC hostages was released late last month in a deal brokered by Venezuelan President Hugo Chavez. They told reporters that Betancourt had been mistreated and kept in chains, had a serious liver problem and was mentally exhausted.

Relations between Chavez and Colombia have deteriorated dramatically since the subsequent killing of FARC commander Raul Reyes in a raid in neighbouring Ecuador, and Venezuela has said it has deployed forces to the Colombian border.

Sarkozy spoke to Chavez on Wednesday and appealed for calm.

"Given the worrying increase in tensions in the Andes region (Sarkozy) repeated his appeal to all countries in the region and all the players involved to show restraint and responsibility so that the path of dialogue and co-operation can be quickly rediscovered," an Elysee statement said.

Betancourt is a former Colombian presidential candidate whose plight has become a major political issue in France. (Reporting by Crispian Balmer; editing by Sami Aboudi)

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