Fidel Castro (search) singled out America's top diplomat in Cuba as he blamed a supposed conspiracy between the U.S. government and exiles in Miami for his recent dissident crackdown and the firing-squad executions of three hijackers.

Pope John Paul II has appealed to Castro to show clemency toward the dissidents, who were sentenced to long prison terms, the Vatican (search) said Saturday.

During a nationally televised address lasting more than three hours Friday night, the Cuban leader accused U.S. Interests Section Chief James Cason (search) of fomenting subversive activities by 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 typically uses such terms for Cuban exiles who actively oppose his rule.

Leaders in Florida rejected Castro's charges.

"Everyone knows he's got no one else to blame but himself," said Rep. Ileana Ros-Lehtinen, a Republican Cuban-American from Miami. "He's the one who calls the shots in Cuba and creates misery on the island. It's all his doing."

"This is just another disgrace from an oppressive regime that continues to deny the people of Cuba the freedom they deserve," Florida Gov. Jeb Bush said in a statement.

Cuba has come under heavy world criticism in recent weeks for sentencing 75 dissidents to prison terms ranging from six to 28 years on charges of collaborating with American diplomats to subvert the socialist system. The dissidents and diplomats deny the charges.

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

In an appeal made through the Vatican secretary of state, Cardinal Angelo Sodano, the pope expressed his "profound pain" over the executions and "deep sorrow" over the other sentences, asking Castro "for a significant gesture of clemency toward those convicted."

The letter was dated April 13 but released only Saturday by the Vatican press office.

"I am sure that you also share with me the conviction that only a sincere and constructive confrontation between the citizens and the civil authorities can guarantee the promotion of a modern and democratic Cuba ever more united and fraternal," the letter from Sodano concluded.

The pope, the first pontiff to visit Cuba in 1998, staunchly opposes the death penalty.

Castro suggested in his speech that the executions were necessary to halt a possible migration crisis.

"The sentences imposed by the tribunals and upheld by the Council of State had to be applied without wavering to the hijackers of the ferry," Castro said.

All other would-be hijackers "should know that they will be undergo extremely quick trials in the appropriate courts," he said. "That is also a tough measure, but necessary because such actions must be yanked out by the roots."

Castro said the hijacking of a DC-3 passenger plane to the United States on March 13 set off a string of at least 29 known cases of planned hijackings.

It was unclear how many of the plans came to fruition, but only three such attempts are publicly known: the successful March 31 hijacking of an airliner to Key West, Fla.; the April 2 ferry hijacking attempt; and the April 10 arrest of a group of men who allegedly planned another airliner hijack.

Castro also used the speech to accuse Cason of provoking his government by hosting the dissidents who were later convicted.

"He came here with instructions to carry out all kinds of provocations against Cuba," Castro said.

The American mission was closed for the weekend and Cason and other U.S. diplomats were not 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 he characterized as "counterrevolutionaries."

The Cuban leader has criticized Cason in the past and has even suggested that he could close 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.

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