Cuba’s President Raul Castro gestures after delivering a speech to members of the National Assembly in Havana, December 20, 2014.

Three men who served long U.S. prison terms for spying received a standing ovation in Cuba’s parliament Saturday, shaking their fists in victory as President Raul Castro declared that detente with Washington won’t change the communist system he leads.

The last imprisoned members of the “Cuban Five” spy ring were freed this week in a sweeping deal that included the liberation of American contractor Alan Gross and a Cuban spy for the U.S. from their jail cells in Cuba, and pledges to restore full diplomatic relations and loosen U.S. restrictions on trade and travel to the island.

U.S. President Barack Obama says the changes are designed to encourage reform in Cuba’s one-party system and centrally planned economy.

Castro rejected that idea in his address to the twice-annual meeting of the National Assembly, saying “we must not expect that in order for relations with the United States to improve, Cuba will abandon the ideas that it has struggled for.”

Castro expressed gratitude to Obama for the “just decision” to release the men who spied on anti-Castro exile groups in South Florida in the 1990s and have long been regarded as heroes in Cuba. Seated behind the three and their families was Elian Gonzalez, the young Cuban rafter at the center of a bitter custody battle in 2000 between relatives in Miami and his father in Cuba.

The president closed his speech with “Viva Fidel!” in reference to his older brother, who has not been seen nor heard from since the historic development was announced on Wednesday, provoking speculation about his health and whereabouts.

While Obama is clearing the way for limited exports to Cuba and freer travel by specific categories of Americans such as academics and artists, Congressional action would be needed to end the decades-old embargo Cuba blames for the dire condition of its infrastructure and economy.

Castro reminded Cubans that the embargo remains in place, particularly limits on international financial transactions that Cuba accuses of blocking its access to credit and international investment.

“An important step has been taken, but the essential thing remains, the end of the economic, commercial and financial blockade against Cuba, which has grown in recent years particularly in terms of financial transactions,” he said.

Castro confirmed he would attend the Summit of Americas in Panama in April, where he is expected to have further discussions with Obama.

His address to the National Assembly follows surprise announcements by both presidents Wednesday that Cuba and the U.S. will reopen embassies and exchange ambassadors for the first time in more than 50 years.

The agreement included the exchange of the three prisoners, convicted in 2001, for a Cuban who had been imprisoned on the island for nearly 20 years for spying on behalf of the CIA. Gross had been held in Cuba for five years for illegally importing restricted communications equipment. Two members of the Cuban Five, Fernando Gonzalez and Rene Gonzalez, already had been released by the U.S. As part of the exchange, Cuba also released 53 other prisoners.

Late Friday, state television showed four of the Cuban Five celebrating their reunion by singing together during a private party in Havana.

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