Washington on Friday urged Colombian rebels to provide proof their hostages were alive, but stopped short of backing Venezuelan President Hugo Chavez in his stymied efforts to mediate in the crisis.
"We continue to call on the FARC [Revolutionary Armed Forces of Colombia] to present proof of life of all hostages," a US State Department spokesman said when asked about Colombian President Alvaro Uribe's decision to end Chavez's mediation for a prisoner-swap deal with the leftist rebels.
"It's a sovereign decision taken by the government of Colombia. We respect their right to make that decision," he said.
Uribe said on Wednesday that he considered Chavez's role as a mediator in the crisis was over because the Venezuelan leader had ignored his demand not to speak directly with Colombian generals about the hostages.
But on Thursday Chavez called on FARC leader Manuel Marulanda to provide proof that 45 prominent hostages are alive, adding any freed hostages would be welcome in Venezuela.
The US official, who asked not to be identified, expressed support for Uribe's efforts to secure the release of the hostages, but failed to echo a call by France for Chavez to continue as mediator.
The US State Department spokesman held FARC responsible for the well-being of all their captives and said "proof of life is a required and necessary step for any credible effort to secure the release of the hostages."
The Uribe administration is trying to strike a deal with FARC, which has offered to release 45 high-profile hostages, including French-Colombian politician Ingrid Betancourt and three Americans captured in 2003 during a US-backed anti-drug operation, in exchange for 500 imprisoned FARC rebels.
French President Nicolas Sarkozy has taken a personal interest in the hostage crisis, especially in seeking the release of Betancourt, kidnapped while running for president in Colombia in 2002.
In the three months that Chavez has sought to pin down the prisoner-swap deal, the US has repeatedly said it welcomed any effort to secure the release of the captives, despite its dislike of the leftist Venezuelan leader and his anti-US rhetoric.
The mother of one of the US hostages said Uribe made a "horrible ... childish" decision in taking Chavez out of the picture and said she now feared the worse for her son, Marc Gonsalvez.
"Maybe Chavez did something a bit wrong, but Uribe got rid of him and now I've heard that he's looking for [the hostages] to try to rescue them so they all get killed," Jo Rosano said, raising the prospect of a botched attempt to rescue them by force.
In a telephone interview from her home in Connecticut, Rosano said she was eagerly waiting for proof that her 35-year-old son was still alive and that she wished Chavez could continue working to free the hostages without Uribe's help.