Speaking at the end of a regional meeting against the North American Free Trade Agreement on Friday, Castro said the assassination was aimed at overthrowing Cuba's communist government.
"We knew that Mr Bush had made a commitment with the mafia of the Cuban-American Foundation to kill me. I say so and I accuse him of this," Castro told some 1000 representatives from 32 nations.
But Cuba's long-serving leader vowed to "go down fighting" if the US tried to invade the country at any time.
Striking a belligerent posture in the course of a five-hour marathon address, Castro said Cuba would resist US machinations.
Speaking of his steely resolve, he said "the deceased can still talk. The deceased can make plans. He is not dead yet."
"And those idiots better not believe we are wasting our time, because we really work at our job. This country will never give up. It will never lay down its weapons," Castro insisted.
He said Cuba does not want "in any way to assume the cost of a war against Yankee imperialism," but warned that despite the tremendous pressure from Washington, "we won't budge at all from our principles."
"I am telling you I don’t want to survive a war. I have already done my part and I still have to do what I have to do. Weapons in hand, I don’t care how I die, but I am confident that if they invade us, I will go down fighting," Castro said.