HAVANA — A lively and healthy-looking Fidel Castro appealed to President Barack Obama to prevent a global nuclear war in an emphatic speech Saturday that marked his first official government appearance since emergency surgery four years ago.

Castro's speech before the Cuban parliament, along with other numerous recent public appearances, raised questions about how much he will resume a leadership role.

Castro, who turns 84 in a week, arrived on the arm of a subordinate, waving and smiling as the crowd applauded loudly in unison.

"Fidel, Fidel, Fidel!" the participants chanted. "Long live Fidel!"

Dressed in olive-green fatigues without military insignias, he immediately took the podium and delivered a fiery 11-minute speech on his fears of an impending global nuclear war. He implored Obama and other wealthy nations to make sure such an event never happens.

Castro then took a seat next to Parliament leader Ricardo Alarcon -- instead of sitting in the chair that parliament members leave empty in his honour during his absence. Current President Raul Castro sat on the other side of the stage, where he listened intensely and took notes as his older brother spoke.

Lawmakers followed the speech with enthusiastic remarks to Fidel Castro about how fully recovered and healthy he appeared. They also commented on the topic at hand.

Asked by one parliamentarian if Obama would be capable of starting a nuclear war, Castro replied, "No, not if we persuade him not to."

He patted his hand on the desk for emphasis, then fell silent, seemingly surprising a crowd long accustomed to the hourslong speeches for which he was famous during his 49 years in power.

Castro's participation in Saturday's legislative session marks the bearded revolutionary's first official government act -- and his first joint appearance with Raul -- since his emergency intestinal surgery in 2006.

It was bound to raise questions about his future role in the government. Even before he confirmed his attendance at this weekend's gathering, top leaders and state media had begun calling him "commander in chief," a title he had largely shunned since relinquishing power.

Fidel Castro was Cuba's unquestioned, unchallenged "maximum leader" for 49 years, starting after his band of rebels toppled Fulgencio Batista on New Year's Day 1959.

Following his surgery, he dropped from sight and ceded power to Raul, five years his junior. Rumours about his health swirled as he remained for years in near seclusion.

Recently, however, the former Cuban leader has been making near-daily appearances in and around Havana: He has addressed groups of Cuban intellectuals and Communist Youth meetings, and even made a trip to the Havana aquarium for a dolphin show.

Castro, who has written on the topic of nuclear war for months, maintains that the United States and Israel will attack Iran and that Washington could also target North Korea. He has suggested the conflict could have Armageddon-like consequences for the whole world, even predicting in several opinion columns that fighting was to already have begun by now.