CARACAS: Venezuelan President Hugo Chavez is in “good spirits” but fighting for his life as he undergoes chemotherapy in a Caracas military hospital, the vice president said Friday, revealing new details about the leftist leader's treatment.

Nicolas Maduro, the leftist leader's political heir, lashed out against a wave of rumours about Chavez's health, accusing the Miami-based Venezuelan diaspora of fomenting them to destabilise the nation.

After the opposition accused him of lying about Chavez's health, Maduro disclosed for the first time that the president began chemotherapy following his fourth cancer surgery in Cuba in December and decided to continue the treatment in Caracas on February 18.

“He has strength that is superior to the treatments that he is receiving and he is in good spirits, battling, receiving his treatments,” he told reporters after a mass for Chavez in a new chapel on the hospital grounds named “hope”.

When he went into the operating room in Havana on December 11, Maduro recalled, Chavez told his aides that there was a “possibility that he would not come out” alive, but he survived it.

At the end of the year, his condition “worsened” due to a respiratory infection and a tracheal tube was inserted to assist his breathing.

But after a “general improvement” of his vital organs in January, the firebrand leader and his doctors in Cuba decided to begin chemotherapy and radiation therapy, the vice president said.

Maduro said that Chavez decided last month to return to Venezuela and told his aides: “I am going to enter a new phase with the complementary treatments, more intense and very difficult, and I want to be in Caracas, so do everything that must be done to return to Caracas in safe conditions.”

Senior officials had spent the day rebuffing rumours that Chavez may be dead or on his deathbed.

Maduro singled out the conservative Spanish newspaper ABC and Colombian radio Caracol, calling them “fascist” news organisations that are part of a “campaign against the stability of Venezuela, lying about Chavez”.

ABC reported on Friday that Chavez was transferred to the presidential retreat in the island of La Orchilada days ago to spend his final moments with his family there.

Radio Caracol interviewed Panama's former ambassador to the Organisation of American States, Guillermo Cochez, who claims that Chavez was taken off life support days ago after being declared brain dead.

Chavez, whose nation sits on the world's largest proven oil reserve, has not come out or spoken in public in almost three months.

The government has only released a set of pictures on February 15, showing him smiling in his sickbed and flanked by two daughters, three days before he returned to Caracas in the dead of night.

The normally garrulous and omnipresent leader's prolonged absence from public view has fueled a slew of rumours on social media and the streets of Caracas.

“There is psychological warfare to confuse the Venezuelan people,” said Science Minister Jorge Arreaza, Chavez's son-in-law.

“Comandante Chavez is fighting,” he said, adding that the firebrand leader was “at the military hospital, very calm with his doctors and his family.”

The government says Chavez remains in charge and that he even held a five-hour meeting in his military hospital room last week, but the opposition has voiced doubts that it ever took place.

“Maduro has lied about the health of the president. It is a lie that he met him for five hours. The country will know the truth in a few days,” opposition leader Henrique Capriles wrote on Twitter.

“We will see how they explain to the country in the coming days all the lies that they have said about the president's situation,” said the Miranda state governor, who lost to Chavez in the October presidential election.

Around 40 university students have spent four straight nights chained to each other in the middle of a Caracas street, vowing to stay there until the “de facto” government “tells the truth” about Chavez.

Under the constitution, an election would have to be held within 30 days if Chavez is declared unfit to return to power. An opposition alliance is holding talks to name a unity candidate in case a snap election is called.

In power for 14 years, Chavez was supposed to be sworn in to a new six year term on January 10, but his inauguration was delayed indefinitely, a decision backed by the Supreme Court.