President Fidel Castro (search) on Friday claimed that a conspiracy between the U.S. government and Cuban exiles in Miami was to blame for his dissident crackdown and the executions of three hijackers.

In a nationally televised address that lasted more than three hours, the communist leader also accused America's top diplomat in Cuba (search), James Cason, of fomenting unrest among opponents of his government.

"The arrest of various dozens of mercenaries who betrayed their homeland for privileges and money from the United States, and the death penalty for common criminals ... were the result of conspiracy stirred up by the government of (the United States) and the terrorist mafia," he said. Castro frequently uses such terms to refer to Cuban exiles living in the Miami area who actively oppose his rule.

Cuba has come under heavy world criticism in recent weeks for holding rapid tribunals and giving the dissidents sentences ranging from six to 28 years on charges of collaborating with American diplomats to subvert the socialist system -- charges that the opponents and U.S. officials deny.

The American government and various Cuban exiles living in the United States have been especially critical of the Cuban actions, expressing outrage and dismissing suggestions of causing dissent in Cuba.

The communist island has received even harsher criticism for the firing-squad executions on April 11 of three men convicted of terrorism (search) charges in the attempting hijacking of a ferry filled with passengers. No one was injured in the hijack attempt.

Castro also used the speech -- his most lengthy public statements yet on the crackdown -- to accuse Cason, the U.S. Interests Section Chief, of provoking his government by hosting the dissidents who were later convicted.

"He (Cason) came here with instructions to carry out all kinds of provocations against Cuba," Castro declared.

The U.S. Interests Section was closed for the weekend and Cason and other American diplomats were not immediately available for comment. But Cason has previously denied provoking Cuban authorities, saying he is simply trying to promote democracy and human rights on the island.

"I'm not out rabble-rousing against the regime," Cason said recently. "I'm giving moral encouragement, visiting people in their homes who have gone to jail for political things and say 'The American people are with you."'

Castro's detailed accounting included the numerous meals, cocktail parties and other gatherings -- complete with dates and names of people in attendance -- that he said Cason hosted for dissidents, who the Cuban president characterized as "counterrevolutionaries" and "mercenaries."

The Cuban leader has criticized Cason in the past and has even suggested that he could shut down the U.S. Interests Section -- the American mission here.

But while stopping short of any major diplomatic action, Castro claimed Cason offered his official residence to dissidents for their meetings, including a March 14 gathering by independent reporters -- some of whom were arrested later -- for a journalism ethics seminar.

Castro said that same night the decision was made to begin rounding up dissidents his government had linked to Cason.

The Iraq war was getting under way that week, and many critics have charged that Castro was simply carrying out a long-planned crackdown when the world's attention was on the Mideast -- charges that Cuban officials have denied.

Castro also mentioned numerous recent hijackings of planes and boats from Cuba to the United States, which his government has repeatedly accused the United States of not doing enough to prevent.

After one of the airliner hijackings Cason in an unprecedented move asked that a statement be broadcast and published by Cuban media, warning that any hijackers hoping to travel to the United States would be dealt with harshly and eventually returned to Cuba.