By Brian Ellsworth and Diego Ore
CARACAS (Reuters) - Venezuelan President Hugo Chavez is improving after a cancer operation in Cuba and has started exercising, officials said on Monday, amid doubts over whether the former soldier is in good enough health to continue governing.
Vice President Nicolas Maduro said he had spoken by phone with Chavez, who was walking and doing exercises as part of his treatment.
"We've gotten the best present we could get this Christmas: a phone call from our commander president," Maduro said on state television.
Information Minister Ernesto Villegas said earlier in the day that Chavez had "shown a slight improvement in his condition," without providing details.
Chavez has not been heard from in two weeks following a fourth operation for an unspecified type of cancer in the pelvic region. The government has said he suffered post-operatory complications including unexpected bleeding and a lung infection, but offered few details about his actual condition.
His death, or even his resignation for health reasons, would upend the politics of the South American OPEC nation where his personalized brand of oil-financed socialism has made him a hero to the poor but a pariah to critics who call him a dictator.
His allies are now openly discussing the possibility that he may not be back in time to be sworn in for his third six-year term on the constitutionally mandated date of January 10.
Opposition leaders say a delay to his taking power would be another signal that Chavez is not in condition to govern and that fresh elections should be called to choose his replacement.
They believe they have a better shot against Maduro, Chavez's anointed successor, than against the charismatic president who for 14 years has been nearly invincible at the ballot box.
But a constitutional dispute over succession could lead to a messy transition toward a post-Chavez era.
Maduro has become the government's main figurehead in the president's absence. His speeches have mimicked Chavez's bombastic style that mixes historical references with acid insults of adversaries.
Opposition leader Henrique Capriles, who lost to Chavez in the October presidential vote, slammed Maduro in an interview published on Sunday for failing to seek dialogue with the opposition at a time of political uncertainty.
"Maduro is not the one that won the elections, nor is he the leader," Capriles told the local El Universal newspaper. "Because Chavez is absent, this is precisely the time that (Maduro) needs help from people (in the opposition camp)."
Chavez has vastly expanded presidential powers and built a near-cult following among millions of poor Venezuelans, who love his feisty language and social welfare projects.
The opposition is smarting from this month's governors elections in which Chavez allies won 20 of 23 states. They are trying to keep attention focused on day-to-day problems from rampant crime to power outages.
(Reporting by Brian Ellsworth; Editing by Sandra Maler)