The pop star, in Buenos Aires on the Latin America leg of her "Sticky & Sweet" world tour, showed up early for a visit Argentine President Cristina Fernandez -- who was then meeting with one of the world's best-known ex-hostages.
Former Colombian presidential candidate Ingrid Betancourt was freed in July after being held more than six years in jungle camps by leftist rebels from the Revolutionary Armed Forces of Colombia. She was visiting Argentina to thank its government for working to free hundreds of other hostages left behind.
Fernandez brought Madonna and Betancourt together for a brief meeting that was closed to the press.
The trip marks Madonna's third visit to Buenos Aires, where in 1996 she played Eva Peron, the first lady of Argentina from 1946-52, in the musiscal film "Evita."
Then-President Carlos Menem permitted her to film one of the movie's most famous scenes on the balcony of the palace, where she sang "Don't Cry for Me Argentina."
Madonna arrived in Buenos Aires with her three children and 200 dancers, technicians and other crew members. She gives the first of four concerts on Wednesday.