Russia and China should not be “subjected to threats of deploying nuclear weapons,” former Cuban President Fidel Castro said in a letter published on his 90th birthday, urging for peace. The iconic socialist leader stressed that no world power has the right to kill millions of people.

On Saturday, Castro attended a gala held in honor of his 90th birthday, although the iconic leader didn’t speak as he sat next to his brother, President Raul Castro, and Venezuelan President Nicolas Maduro.

“Great powers like China and Russia can’t be subjected to threats of deploying nuclear weapons. They are people of great courage and intelligence,” Castro said in his letter, which was published on the website of the Official Body Central Committee of the Communist Party Of Cuba.

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“Mankind is faced today with the greatest danger in its history,” he wrote. “We must preserve peace around the world and must not let any world power believe it has the right to kill millions of human beings,” Castro added.

The former Cuban president also took the opportunity to slam a speech US President Barack Obama made in Hiroshima during a May trip to Japan in which he failed to apologize to the Japanese people.

“I believe that the speech lacked apologetic words for the killing of hundreds of thousands of people in Hiroshima, although he knew about the effects of the bomb. The attack on Nagasaki was equally criminal,” Castro said.

Castro also recalled confrontations with the US during his 47 years in power, as well as CIA plots to assassinate him. Castro also reminisced about his childhood and youth in eastern Cuba, as well as his father’s death.

“I laughed with the Machiavellian plans several US presidents had to eliminate me in any way,” said the Cuban leader.

Castro also thanked all of his supporters for all their good wishes: “I want to express my deepest gratitude for the shows of respect, greetings and praise that I’ve received in recent days, which give me strength to reciprocate with ideas that I will send to party militants and relevant organizations,” he wrote in his letter.

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Castro led Cuba from 1959 until 2008, when he was forced to step down after suffering a severe gastrointestinal illness.

Castro last spoke to the public in April, when he closed the congress of the Cuban Communist party, which is held every two decades. During his speech, the father of the Cuban revolution urged the country to remain true to its socialist ideals when adopting policies to normalize relations with the US.

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