A fourth hostage, Jorge Gechem, a former Colombian congressman, could also soon be freed, Kouchner was quoted by Reuters as saying.
On Thursday Kouchner will meet Alvaro Uribe, the Colombian president, in the capital Bogota.
The Revolutionary Armed Forces of Colombia (Farc) have been holding about 40 foreign hostages for the past few years.
Earlier this month a statement read on Colombian television said the group planned to free the three hostages because of poor health.
|Gonzalez, second from left, was freed by |
Farc earlier this year [AFP]
The group has demanded that 500 of its fighters be freed and called for the demilitarisation of two zones in the south of Colombia.
Uribe has indicated a willingness to negotiate an exchange of prisoners but has ruled out demilitarisation of such a large and populated part of the country - suggesting a smaller, less inhabited zone instead.
Farc's hostages include Ingrid Betancourt, a former Colombian senator who also holds French citizenship who was kidnapped in 2002.
She was seen in footage released last November, apparently being held in chains.
Three American contractors are also being held hostage.
Two Colombian legislators, Consuelo Gonzalez and Clara Rojas, were released last month after an agreement brokered by Chavez.
However, the Venezuelan president angered Colombia when he said that Farc should not be labelled as a terrorist group.