Garcia Marquez has also condemned the use of the death penalty
More than 160 writers, artists and actors from across the Americas and Europe have signed a declaration in support of the Cuban Government.
Colombian writer Gabriel Garcia Marquez and Hollywood actor Danny Glover were among the figures to sign a message condemning "harassment of Cuba", which was read out at May Day celebrations in Havana.
International criticism of Cuba continues after it jailed 75 dissidents for terms of up to 28 years in April following summary trials, and executed three failed hijackers shortly afterwards.
Reporters Without Borders described Fidel Castro's state as "the world's biggest prison for journalists" in a global report issued this week.
TAKING A STAND ON CUBA
May Day message of support signed by:Writers Gabriel Garcia Marquez, Luis Sepulveda and Nadine Gordimer; film director Pedro Almodovar; actor Danny Glover; Nobel peace prize winners Rigoberta Menchu and Adolfo Perez Esquivel
Spanish condemnation signed by:Film director Pedro Almodovar; singers Joan Manuel Serrat, Ana Belen and Victor Manuel
Days earlier, a group of Spanish artists issued a statement condemning the arrests of the dissidents and the executions.
President Castro defended his April crackdown at a huge May Day rally, saying Cuba had to protect itself against the United States.
"We do not want the blood of Cubans and Americans to be shed in a war," he added.
The two-paragraph message of support appeared to condemn US foreign policy without referring to it by name.
"A single power is inflicting grave damage to the norms of understanding, debate and mediation among countries," it said.
"At this very moment, a strong campaign of destabilisation against a Latin American nation has been unleashed. The harassment of Cuba could serve as a pretext for an invasion."
Whilst supporting national sovereignty, the message does not specifically express support for Mr Castro's policies.
The April crackdown - which saw the imprisonment of such prominent dissidents as Hector Palacios, Paul Rivero and Oscar Elias Biscet - has cost Cuba some of its traditional support.
The Cuba Policy Foundation - a Washington group which campaigned for the ending of the embargo against Cuba - disbanded in protest.