Politics and pop stardom mingled in Argentina when former Colombian hostage Ingrid Betancourt and singer Madonna met in Buenos Aires.

The two women - icons for very different spheres of activity - were hosted by Argentine President Cristina Kirchner in her official palace late on Tuesday.

Betancourt, a 46-year-old former presidential candidate who was freed in July after six years' captivity by Colombia's FARC rebels, was in Argentina as part of a South American tour meant to highlight the plight of hostages still in the FARC's hands.

Madonna, the 50-year-old US entertainer who once played former Argentine first lady Evita Peron in a Hollywood musical, was in town for her Sticky and Sweet concert tour.

She went in to greet Betancourt after a meeting between the latter and Kirchner had ended.

After that encounter, Betancourt spoke to journalists, saying she wanted to give a Christmas message to FARC hostages.

"Christmas is coming and I know that the suffering is growing. But I am there with you. Your chains are mine. I am absolutely sure we will bring about your liberation," she said, her voice breaking.

She said that Kirchner was also "going to keep fighting for you as she has fought from the beginning for all of us. Argentina has adopted us and the Latin American continent is going to rise up for your freedom."

Betancourt, who was freed in a Colombian military operation along with 14 other detainees, has vowed from her new home in France - where she also has citizenship - to do all she can to secure the release of the estimated other 700 hostages still held by the Revolutionary Armed Forces of Colombia (FARC).