Vice President Nicolas Maduro surprised Venezuelans with a Christmas Eve announcement that President Hugo Chavez is up and walking two weeks after cancer surgery in Cuba, but the news did little to ease uncertainty surrounding the leader's condition.

Sounding giddy, Mr Maduro told state television Venezolana de Television that he had spoken by phone with Mr Chavez for 20 minutes on Monday night.

It was the first time a top Venezuelan government official had confirmed talking personally with Mr Chavez since the December 11 operation, his fourth cancer surgery since 2011.

"He was in a good mood," Mr Maduro said. "He was walking, he was exercising."

Chavez supporters reacted with relief, but the statement inspired more questions, given the sparse information the Venezuelan government has provided so far about the president's cancer.

Mr Chavez has kept secret various details about his illness, including the precise location of the tumours and the type of cancer. His long-term prognosis remains a mystery.

Dr Michael Pishvaian, an oncologist at Georgetown University's Lombardi Cancer Centre in Washington, said it was an encouraging sign that Mr Chavez was walking, and it indicated he would be able to return to Venezuela relatively soon. But he said the long term outlook remained poor.

"It's definitely good news. It means that he is on the road to recover fully from the surgery," Mr Pishvaian said in a telephone interview.

"The overall prognosis is still pretty poor. He likely has a terminal diagnosis with his cancer that has come back."