Cuban President Fidel Castro warned the United States on Saturday against plotting to kill his most important ally, Venezuela's leftist President Hugo Chavez. "I say to world public opinion: if they assassinate Chavez, the responsibility will fall squarely on the president of the United States, George W Bush," Castro said. The Cuban leader, who was the target of CIA assassination plots after his 1959 revolution steered Cuba toward Soviet Communism, gave no evidence that Chavez's life was in danger. But he said the United States would be responsible for killing Chavez even if the Venezuelan military was to carry out the assassination. He added: "If they can eliminate him, they will." Populist Chavez has led oil-rich Venezuela into a close alliance with Cuba, raising fears in Washington of Cuban-style communism taking hold in the South American country, a major supplier of oil to the United States. Castro, 78, boasted that he had survived at least 100 attempts on his life. CIA plots against him included such capers as poisoned cigars, an exploding conch shell and toxin to make his beard fall out. "This comes from a survivor. I have survived," he said in a nearly six-hour speech that lasted into the early hours of Saturday.