CARACAS: Venezuela's main opposition movement called on the government Wednesday to tell “the truth” about President Hugo Chavez's health as one of his closest allies said his condition was “very worrying.”

More than three weeks after undergoing his fourth round of cancer surgery in Havana, political pressures mounted in this oil-rich nation amid growing doubts about Chavez's condition and no clear succession process established should he die or become incapacitated.

The head of an opposition umbrella group, the MUD, accused the government of “outlandish irresponsibility” in trying to make it appear that Chavez was exercising his duties as president as he underwent a difficult recovery in Cuba.

“It is essential that the government act in a manner that gives confidence. It is essential that it tell the truth,” said Ramon Guillermo Aveledo.

He demanded that the government provide “a diagnosis and a medical prognosis” on the 58-year-old president's condition.

Bolivian President Evo Morales, a close Chavez ally, spoke with the Venezuelan leader's family and later told reporters that “our brother President Chavez's situation is very worrying.”

”Let's hope our prayers will be effective in saving the life of our brother President Chavez,” he said.

Vice President Nicolas Maduro said in a television interview from Havana Tuesday that Chavez was conscious and fully aware “of how complex the postoperative condition is.”

But Maduro provided few specifics about the president's health even as he accused the Venezuelan right of deliberately spreading what he said were sick lies and rumors about Chavez's condition.

Meanwhile, a cascade of rumors swept social networks and Internet blogs, with some claiming Chavez was dead and others on life support.

Maduro, who said he had spoken twice with Chavez during a three day visit to Havana, was returning to Caracas Wednesday to face the brewing crisis in a nation that has the world's largest proven oil reserves.

At the top of his to-do list will be to sort out what happens if Chavez, 58, is unable to be sworn in to a new six year term on January 10 following his re-election in October.

Before leaving for Cuba, Chavez had named Maduro as his choice to succeed him but after having dominated national life here for 14 years his departure from the scene was expected to leave an unsettling power vacuum.

The Venezuelan constitution calls for new elections within 30 days if the president-elect is unable to take the oath of office.

It was also unclear whether Maduro, who was appointed vice president by Chavez after his reelection in October, could remain in office after January 10.

“On January 10 a new constitutional term begins. If the president shows up, he shows up. If the president does not show up, the president of the National Assembly is in line to assume the presidency temporarily, according to the Constitution,” said Aveledo.

The head of the national assembly is currently Diosdado Cabello, the leader of a Chavista faction and said to be a potential political rival of Maduro.

If new elections are held, opposition leader Henrique Capriles, who gave the comandante a good run for his money in the October election, might prevail and seek to begin a new era.

Less than two years ago, it would have been impossible to imagine the country without the larger-than-life Chavez at the helm.

His outsized personality and bombastic style of governing did not permit the ascension of a heir apparent within his United Socialist Party of Venezuela.