Venezuela's President Hugo Chavez has suffered a new setback after cancer surgery in Cuba, raising new fears about his political future, Vice President Nicolas Maduro said Sunday.

"We have been informed of new complications that arose as a consequence of the respiratory infection we already knew about," Maduro said on state TV and radio from Havana. Cuba is Chavez's closest regional ally.

"President Chavez's condition is still delicate," Maduro added, warning that the complications "are being treated in a process that is not without its risks."

Chavez, the face of the Latin American left for more than a decade and a firebrand critic of US "imperialism," has been in power since 1999 in Venezuela, an OPEC member that sits on top of the world's largest proven oil reserves.

Maduro, who said he had spoken with Chavez about his health complications and national affairs, added that the president was facing a "tough situation."

"Comandante Chavez particularly wanted us to relay his New Year's greeting to every Venezuelan family who are gathered together across the country at this time," Maduro said.

The vice president said he would stay in Havana in the coming hours Chave and his family to "closely" follow his progress.

"We trust that the global outpouring of love" for the Venezuelan leader will help him heal, said Maduro.

He was in Cuba with Rosa Virginia Chavez -- one of the president's daughters -- Science and Technology Minister Jorge Arreaza and top Prosecutor Cilia Flores.

Chavez, 58, won another six-year term in October's presidential election, and is scheduled to be sworn in on January 10.

But his health has raised concerns over the future of his leftist movement -- and whether he will even be well enough to attend the inauguration.

Under Venezuela's constitution, a presidential election must be held within 30 days if the president is incapacitated or dies before his inauguration or within the first four years of his term.

On Monday, the government said there had been a "slight improvement" in his condition as he recovers from post-operative respiratory infection.

Officials have never disclosed the type or severity of Chavez's cancer, first diagnosed in June 2011, and he only designated a political successor -- Maduro -- earlier this month.

The longtime Venezuelan leader had, in fact, asserted before embarking on his arduous re-election campaign earlier this year that he was cancer-free.

But he was later forced to admit he had suffered a relapse.

In an announcement made in Caracas before his departure, Maduro did not specify how long the group would stay in Havana. But he said Electricity Minister Hector Navarro would assume the vice presidency during his absence.