Fidel Castro, the former Cuban leader, has delivered his first speech to the national assembly since resigning over ill health four years ago.
The chamber erupted into applause at the sight of Mr Castro, dressed in his familiar olive-green fatigues but without his comandante's insignia.
In an uncharacteristically short speech of just over 10 minutes, he urged the US not to allow a war with Iran.
His brother Raul, who succeeded him as president, sat at his side as he spoke.
It was the first time the two had appeared together in public since Fidel Castro stepped down in 2006.
The speech was a solid, polished performance, Mr Castro's voice stronger than at any point since he re-emerged into public life, the BBC's Michael Voss reports from Havana.
Mr Castro arrived in the chamber on the arm of a subordinate, waving and smiling as the crowd applauded loudly in unison.
In the past, his speeches ran to hours.
After Saturday's address, he sat on for about an hour and 10 minutes, listening to questions from deputies on foreign affairs and responding to them.
The former president warned of the risk of a "nuclear holocaust" involving the US and Iran.
He accused the US of planning to attack Iran and North Korea and urged President Barack Obama to prevent such a conflict happening.
Iran has been accused by the US and others of seeking to develop illegal nuclear weapons - an allegation Tehran denies.
"If war breaks out the current social order will suddenly disappear and the price will be infinitely greater," Mr Castro said.
Asked by one deputy if Mr Obama would be capable of starting a nuclear war, Mr Castro replied: "No, not if we persuade him not to."
Despite his health problems, Fidel Castro is still first secretary of the Cuban Communist Party and has become more active in the last month, giving television interviews and talking in public to selected groups.
Observers are watching the body language between Fidel and Raul Castro closely, reports the BBC's Michael Voss in Havana.
But Culture Minister Abel Prieto told the BBC before the speech that Fidel Castro was not about to re-enter the government.
"I think that he has always been in Cuba's political life but he is not in the government," he said.
"He has been very careful about that. His big battle is international affairs."
Raul Castro, 79, has himself dismissed any suggestion that there is a divide in the Communist Party leadership over the direction of policy, particularly as his government attempts to liberalise parts of Cuba's state-run economy.