News of the pardons provoked riots in Panama City

The move was expected after Panama's President Mireya Moscoso pardoned the four, who were being held on charges of forgery and threatening security.

They had not been charged with attempted murder for lack of evidence.

Ms Moscoso, who is due to leave office next week, said she feared the four would be extradited and executed.

Three of the men who are Cuban-born US citizens flew directly to Miami where they were met by their families while leftist students rioted in Panama City.

The Cuban government described the pardon as "an affront to the victims of terrorism and their families" and described Ms Moscoso as an "accomplice and protector of terrorism".

However, the BBC's Stephen Gibbs reports from Havana that the rupture may be short-lived as the Panamanian leader's successor, Martin Torrijos, has publicly opposed the pardons and said he would work to repair relations.

The president-elect is due to take office next Wednesday.

Summit plot

The four men - all Cuban emigres - were convicted and jailed in April for threatening public security and falsifying documents.

Moscoso announced the pardons before leaving office

Luis Posada Carriles, Gaspar Jimenez, Guillermo Novo and Pedro Remon were on a list of presidential pardons announced by Ms Moscoso.

At a summit in Panama in November 2000, Mr Castro alleged there was a plot to kill him.

Six men were arrested - five Cubans and a Panamanian.

Explosives were found in a case, but the anti-Castro activists denied plotting to kill the Cuban leader.

The defendants said they were in Panama to help a Cuban general who had supposedly planned to seek political asylum.

Wanted men

Earlier this year, Cuba said the sentences handed out to the men, of seven and eight years, were too lenient.

Cuba had tried, but failed, to extradite some of the Cuban exiles, including the alleged ringleader, Luis Posada Carriles, 76, who has been wanted by Havana for many years.

Mr Posada Carriles is a former CIA operative who has long sought the overthrow of Fidel Castro.