Castro, 80, handed power to his brother Raul Castro, 75, in late July as he recovered from what is described as gastrointestinal surgery.

The Cuban leader, who first took power in 1959, has since only been seen in official Cuban television and newspaper images, though he has met some few visitors in Havana.

In Tuesday's phone call Castro came across as energetic and enthusiastic as he commented on the day's news.

"Hello there, illustrious and dear friend, how are you?" Castro asked Chavez at the start of his 25-minute telephone call on the Venezuelan leader's "Hello President" show.

"What joy hearing your voice, and knowing you are well," Chavez replied.

"I am making progress, I feel more energetic, with more strength and more time to study," Castro said. "I am have gone back to being a student."

The Cuban leader encouraged those concerned about his recovery to be patient.

"I urge everyone to be patient, calm, and to be happy, if everyone is calm, the country keeps moving forward, which is the important thing... I also ask for tranquility for myself to be able to get my new duties done," he said.

But "I cannot be talking every day and get into the habit of making news every day."

Still, Castro made a point of saying he was "very informed about the dangers of wars, climate change, food supply troubles, because as you (Chavez) have noted, millions of people are going hungry."

The two leaders discussed global warming and other news, including Venezuelan issues.

Chavez joked that Castro has turned him into "a sort of emissary or bridge -- whoever wants to know how Fidel is doing comes here, calls me, and I always tell them the truth," Chavez said.

Cuba's communist government has treated the state of Castro's health as a state secret.

The latest Cuban television footage of Castro, broadcast in late January, appeared to support official claims his recovery from surgery was going well.

The January 30 images show Castro in apparent good spirits and looking healthier than in the previous footage broadcast on October 28.

He was shown chatting with Chavez, and saying his recovery from surgery was "far from being a lost battle."

Senior US officials have not been so optimistic about their Cuban foe's longevity.

Earlier in January, then US spy chief John Negroponte said "Castro's days or months seem to be numbered."

And Tuesday, the new director of national intelligence, Michael McConnell, said: "This year is likely to mark the end of Fidel Castro's domination of Cuba."

But McConnell added that "significant, positive change is unlikely immediately following his death."

"The period following his July operation afforded Raul Castro the opportunity to solidify his own position as successor."

As acting president, Raul Castro twice called for dialogue with the United States, but Washington, which has dismissed him as "Castro light", insisted Cuba must first adopt democratic reforms.

Commerce Secretary Carlos Gutierrez, who co-chairs the official Commission for Assistance to a Free Cuba, said last week that Washington has no intention of ending its 45-year-old unilateral trade embargo on the island.

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