In a message posted on a website often used by the Revolutionary Armed Forces of Colombia (Farc), a senior leader of the group ruled out any early release of Betancourt until the government frees rebel prisoners.
Rodrigo Granda, the rebels' foreign relations chief, said those held would be freed "only as a result of a prisoner exchange", the statement on the website said.
'Reactivate the path'
Chavez, who helped broker the release of six Farc hostages earlier this year, said he could not assist further unless there were gestures from the US and Colombia in order to "reactivate the path" to the hostages' release.
The moves came as Betancourt's sister, Astrid, criticised the Colombian government, saying it had used rumours of her sister's ill health to justify increasing its military presence in the rebel-controlled area where she is being held.
Colombian military officials have said that additional troops have been sent to the southeast of the country where the rebels and their hostages are thought to be holed up, but have not given numbers.
"It's not a good thing. That puts the lives of the hostages at risk and
doesn't at all contribute to a climate of confidence necessary for the Farc to move forward,'' she said.
Betancourt, a former Colombian presidential candidate who has been held captive for six years, was said by her son earlier this week to be dying from hepatitis B and a skin disease.
He said she was desperately in need of a blood transfusion.
Hundreds of hostages
The Farc is thought to hold about 40 foreign hostages, including three US Pentagon contractors, as well as hundreds of Colombian hostages.
Efforts to free the hostages have been complicated by death of two senior Farc leaders, including Raul Reyes, who was killed in a cross border raid into Ecuador by Colombian forces on March 1.
Several other Farc fighters were killed in the incident.
Last week the Colombian government offered an amnesty for Farc rebel prisoners in return for the hostages' release, however the group has said it wants a large area of the country to be demilitarised before any negotiations take place.
The group has been fighting a bloody civil war against the government and paramilitary groups for decades, in which thousands have died.