By ALFONSO CHARDY

  Three men who attempted to hijack a passenger ferry to Florida last week were executed at dawn Friday after summary trials in Cuba, the government
  announced in Havana.

  The men were charged with ''very grave acts of terrorism'' and sentenced at the summary trials on Tuesday, according to an official statement read on
  Cuban state television. The men appealed -- but the sentences were upheld by Cuba's Supreme Tribunal and the ruling Council of State and were carried
  out at dawn Friday, the statement said. Executions in Cuba are generally carried out by firing squad.

  The executions were the first of Cubans accused of terror charges in more than 10 years. An exile from Miami, Eduardo Díaz Betancourt, was executed in
  January 1992 after being found guilty of terrorism, sabotage and enemy propaganda. Díaz Betancourt had been arrested while on a mission to infiltrate
  Cuba allegedly to stage acts of anti-government sabotage.

  Executions of criminal suspects are relatively frequent in Cuba, but the executions of the three hijack suspects come at a time of heightened tension in
  Cuba highlighted by a massive crackdown against dissidents that has resulted in the arrests of scores of opponents in recent weeks.

  In Washington, a State Department official said the U.S. government was looking into the report of the executions and planned a statement later. On
  Thursday, Secretary of State Colin Powell condemned Cuba for the dissidents' arrests.

  Cuban exile leaders in Miami were furious.

  ''They have murdered these poor people,'' said Joe Garcia, executive director of the Cuban American National Foundation. ``The summary trial and an
  execution without due process is murder and the U.S government should indict Fidel Castro and his brother, Raúl Castro and all the other thugs that
  govern that island.''

  Cuban experts in Miami said the executions and the arrests of dissidents symbolically marked the start of a period of harshness in the island. Jaime
  Suchlicki, director of the Institute for Cuban and Cuban-American Studies at the University of Miami, said the crackdown may be part of an effort by Fidel
  Castro to eliminate opposition.

  ''The crackdown has to do with a plan by Castro of ending the opposition and pave the way for his brother and succession in Cuba,'' Suchlicki said.

  Castro has repeatedly said that his brother Raúl, the minister of defense, will be his successor when he dies or steps aside.

  ''There are indications that this is the beginning of a very harsh period of repression,'' Suchlicki said.

  Besides those executed, another four men allegedly involved in the hijack attempt received life sentences, the Cuban government said.

  No one was hurt when the group, reportedly armed with at least one pistol and several knives, seized the ferry and its 50 passengers in Havana Bay April
  2 and ordered the captain to sail to the United States.

  Later that day, the 45-foot ferry Baragua ran out of fuel in the high seas of the Florida Straits, and officers on two Cuban Coast Guard patrol boats that
  chased them there tried to persuade the hijackers to return to the island.

  The hijackers allegedly threatened to throw passengers from the boxy, flat-bottomed boat overboard but soon agreed to let the ferry be towed 30 miles
  back to Cuba's Mariel port for refueling.

  After the ferry was docked in Mariel, west of Havana, Cuban authorities eventually gained control of it April 3 and arrested the suspects after a
  quick-thinking French woman hostage jumped into the water to confuse her captors.

  The standoff ended with all the hostages, then the suspects, jumping into the water.

  The Baragua was hijacked a day after a Cuban passenger plane was hijacked to Key West, Fla., by a man who allegedly threatened to blow up the aircraft
  with two grenades. The grenades turned out to be fake.

  Ten of the Cubans aboard that flight opted to remain in the United States and 19 others asked to go home.

  Another Cuban plane was hijacked to Key West less than two weeks earlier.

  The hijackings coincided with a crackdown on dissidents in Cuba and rising tensions with the United States.

  Material from The Associated Press was used to supplement this report.