Colombia's government said Wednesday that it was canceling Venezuelan President Hugo Chavez's mediation role with leftist rebels in a possible hostage swap.

President Alvaro Uribe's press secretary said the decision was made because Chavez directly spoke with the head of Colombia's army earlier in the day about the state of hostages held by the Revolutionary Armed Forces of Colombia, or FARC.

In calling the army chief, Gen. Mario Montoya, Chavez defied Uribe's order that the Venezuelan leader not speak with Colombian military leaders about the issue, said Cesar Mauricio Velasquez, the presidential spokesman.

The news was announced late Wednesday in a hastily convened news conference.

The FARC, Latin America's most potent rebel army, holds some 45 high-value hostages, including three U.S. military contractors and Ingrid Betancourt, a former presidential candidate and dual Colombian-French national who has become a cause celebre in France.

For their release, the FARC is demanding the government release all imprisoned rebels, who number in the hundreds.

In a brief statement, Velasquez did not elaborate on why Uribe had ordered Chavez not to speak to Colombian military officials.

Chavez began the mediating process in August and even hosted a top FARC leader in the Venezuelan capital of Caracas on Nov. 8.

But the FARC has so far failed to produce proof-of-life for any of the high-value hostages, as sought by the Colombian and U.S. government.

On Monday, Chavez said Uribe had told him he was prepared to meet with the aging leader of the FARC, Manuel "Sureshot" Marulanda. In response, Uribe said he those comments were made in confidence and placed a Dec. 31 time limit on Chavez's mediation efforts.

As late as Wednesday afternoon, however, Colombian government officials were praising the mediation role of Venezuela's socialist leader.

"Chavez is playing an excellent role and for that we are grateful," Luis Carlos Restrepo, the government's chief peace negotiator, said in an interview with The Associated Press.