Former Cuban dictator Fidel Castro made a bold public appearance Friday, warning thousands of students at the historic University of Havana of what he believes is the world's looming nuclear threat.

The 35-minute speech was the most public of Castro's recent appearances, which have occurred mostly privately and to small groups.

Former Cuban leader Fidel Castro speaks during a meeting with students at the University of Havana on Friday. (Desmond Boylan/Reuters)It was also the first time the revolutionary leader donned his full military uniform since stepping down as president four years ago because of illness.

Images of him in the olive-green cap and uniform — minus the star and laurels he held as commander in chief — will surely revive speculation the 84-year-old is seeking a larger role in Cuban politics after turning power over to his younger brother Raul.

Speaking to students assembled on and in front of the school's majestic stairway, Castro repeated his warning that the world stands on the brink of a nuclear conflagration due to tension pitting the United States and Israel against Iran. He has returned to the message almost daily since emerging from seclusion in July.

Castro — who began his political career as a student activist at the same university 60 years ago — said it has fallen to his tiny island to warn the world of the looming nuclear threat, and that it was important that it did not fail.

"Faced with the skeptics, our duty is to keep up the fight," Castro said. "I am convinced that a good number of people are becoming conscious of the reality."

He thanked the university students for their support, saying he has always appreciated their backing.

Coming out of the shadows

"In this, like in many battles of the past, we can win," he said of his efforts to warn the world of the nuclear danger.

Castro stepped down — first temporarily, then permanently — in July 2006 after a serious illness that nearly killed him. He stayed almost entirely out of the public eye for four years while his 79-year-old brother, a close partner in the 1959 revolution, took the reins of power.

Since bursting back on the scene in July, the elder Castro has scrupulously avoided mention of domestic issues such as Cuba's economic woes or its fight against corruption — presumably to avoid stepping on Raul Castro's toes. He did the same on Friday, limiting himself to reminiscing about the past and warning about a nuclear future.

But Fidel's speeches have grown bigger, and he has crept closer and closer to at least looking like the revolutionary leader he once was. While he is no longer president, Fidel remains head of Cuba's Communist party.

After wearing a loose-fitting track suit in several early appearances, Fidel caused a stir by donning an olive-green shirt at a July 24 ceremony outside Havana.

When he addressed Cuba's parliament two weeks later, he was wearing the top half of his military fatigues. On Friday, he looked completely the part of a revolutionary, decked out head-to-toe in his military uniform, with a simple military cap to shield him from the sun.