Former Cuban President Fidel Castro has delivered a major public speech, warning students at the University of Havana that the world stands at the brink of nuclear war.

Mr. Castro wore his trademark green army fatigues and hat as he spoke early Friday. He warned that tensions between the United States, its ally Israel and Iran are leading to a nuclear confrontation.

The state-run news agency, Granma, said Mr. Castro noted that during World War II, the U.S. became the first country to attack another nation using nuclear weapons. He said the current U.S. nuclear arsenal has many times more destructive power than those earlier weapons.

Mr. Castro has been seen publicly several times in the past month, after years of seclusion following intestinal surgery and ceding power to his brother, Raul, in 2006.

In his speech Friday, the elder Mr. Castro said that the possibility of nuclear war and the danger it poses to humanity should lead every person on Earth to do what he or she can to avoid such a catastrophe.

The former president, who recently turned 84, has made similar warnings about the growing nuclear threat in recent public appearances.

Last month, he addressed the Cuban parliament, and warned how increasing tensions between the United States and Iran could lead to nuclear war.

Mr. Castro also unveiled a new book last month enitled The Strategic Victory. The memoir is focused on the Cuban Revolution, which brought him to power more than 50 years ago.

Raul Castro formally assumed the presidency in February 2008.

Some information for this report was provided by AP, AFP and Reuters.