HAVANA — Cuban President Fidel Castro is defending his crackdown on dissent, shrugging off international criticism and promising to defend his country against destabilizing moves by the United States.

"We are now immersed in a battle against provocations that are trying to move us toward conflict and military aggression by the United States," Castro said.

He did not directly refer to Friday's execution of three men convicted of trying to hijack a ferry to the United States, in a Friday night speech broadcast on Cuban television.

Nor did he mention the lengthy sentences given 75 dissidents convicted of helping U.S. diplomats undermine Cuba's socialist system.

Castro made it clear he considers his country under U.S. attack and he will do whatever it takes to ensure his system remains intact.

"We have been defending ourselves for 44 years and have always been willing to fight until the end," Castro said.

"If someday they make us disappear from the map, we will die with the greatest dignity in the world."

Some longtime Cuba observers believe Castro is alarmed by the U.S. government's military action in Iraq and worries his country could be next.

"I think that the Cubans have looked at what is happening in Iraq and have concluded that the United States will not be restrained by international law and international institutions," said Cuba specialist Wayne Smith, who was the top U.S. diplomat in Havana during former president Jimmy Carter's administration.

Smith said he considers such a strike unlikely but "the Cubans still need international support from the Europeans, from Canada" and what they are doing is "only shooting themselves in the foot."

The Cuban government's harsh measures began March 18 -- the eve of the launch of the U.S.-British invasion of Iraq. That night, a statement read on state television announced a roundup of "mercenaries" was underway.

Over the following three weeks, authorities arrested, tried and sentenced 75 of its most vocal critics to terms ranging from six to 28 years.

Authorities accused those arrested of receiving money from and working with U.S. diplomats to harm Cuba's economic and political systems -- charges the dissidents and Americans deny.

The crackdown came amid a rash of hijackings of planes and a ferry, which Cuba blames on U.S. policies it said encourage illegal migration.

On Friday, a firing squad executed three men arrested in the unsuccessful armed hijacking of a passenger ferry April 2. Four others were sentenced to life in prison.