Former Cuban leader Fidel Castro, wearing his green military cap and clothing like the comandante of old, made his first speech before the Cuban public on Friday since falling ill in 2006, warning of the threat of nuclear war.

Castro, 84, spoke from the same steps of the University of Havana where 60 years ago he stirred fellow students to political action in the beginnings of the revolution that eventually put him in power in 1959.

About 10,000 people, mostly students, filled the steps and nearby streets to listen to the man who led Cuba for 49 years before an intestinal illness forced him to resign as president and, as Castro stated in a recent newspaper interview, nearly killed him.

His speech was the latest in a string of appearances since Castro re-emerged in July from four years of seclusion. As he has all summer, Castro warned that nuclear war is inevitable if the United States, in alliance with Israel, tries to enforce international sanctions against Iran over its nuclear program.

The crowd shouted Fidel, Fidel Fidel and applauded at several points during the nationally televised address.

Standing behind a podium at the top of steps, he spoke for about 40 minutes, far shorter than the hours-long speeches he once gave. As has been his custom since resurfacing, he did not talk about Cuba's domestic issues.

His renewed public presence has raised questions about whether he could resume a larger role in running Cuba, now officially led by his younger brother, President Raul Castro.

'THE SURVIVAL OF HUMANITY'

He slammed the United States, his long-time foe, for creating a system that threatens the survival of humanity.

The problem of people today, the more than 7 billion human beings, is to prevent such a tragedy from happening, he said.

In this, as in many struggles in the past, it is possible to be victorious, he said.

Last month, he spoke to a session of the National Assembly about the possibility of nuclear war.

He wore plain military clothing, without military insignia or stars.

Fidel Castro ceded power to his brother after undergoing surgery in July 2006, then officially resigned as president in February 2008.

He remains head of the ruling Communist Party and plays a significant behind-the-scenes role. But there has been no sign that his brother is not in charge of the government.

The president did not attend his brother's speech.

Students said they came to the speech not just to hear Castro's message but also for the chance of seeing the elderly revolutionary who has been a world figure for the past half century.

Their theories about why he has stepped back into the spotlight ranged widely, with most taking him at his word that he feels compelled to warn of a possible U.S.-instigated war.

Fidel is a source of pride for all Cubans. His appearances show the United States that he's still standing, said dental student Eileen Mendoza.

This is a historic act, said economic student Jose Gonzalez Abreu. Maybe he's preparing to return to the kind of big, historic speeches he gave before he fell ill.

Raul Castro, 79, has lately stepped up the pace of small economic reforms he has initiated to revive Cuba's struggling economy and, in his words, assure the survival of the revolution after its current generation of leaders is gone.

(Additional reporting by Nelson Acosta; Editing by Frances Kerry and Will Dunham)

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