Colombian President Alvaro Uribe has offered a €1.6 million reward for information on hostages held by Marxist paramilitaries.
Mr Uribe, a Washington ally, has driven back the rebels, but the release of hostages, including former presidential candidate Ingrid Betancourt, is one of the more sensitive challenges for his government.
After his May re-election, Mr Uribe softened his position about talks over hostages with the Revolutionary Armed Forces of Colombia, or Farc.
But a bomb attack officials blamed on the Farc last week prompted him to suspend negotiation efforts and order troops to rescue the kidnap victims.
The Farc, which wants rebel prisoners exchanged for 62 key hostages, has fought for four decades and says it wants to install a socialist state.
Families of hundreds of kidnap victims protested in the capital Bogota this week to demand Mr Uribe halt efforts to seek a military solution and negotiate to release the hostages.
Since his election in 2002, Mr Uribe has reduced violence by sending troops to retake the urban areas and highways from rebels. He has also demobilised thousands of illegal right-wing paramilitary fighters who once battled with Farc.