Although Cuban President Raul Castro has praised recent progress in U.S.-Cuba relations, the communist leader demanded that the United States respect its political system.

Recently, the two countries began working toward normalizing diplomatic ties after decades of a frozen relationship. President Barack Obama also announced a "new chapter" in U.S. ties with the country on Wednesday.

Obama also said that the U.S. government will push Cuba on issues of human and political rights when they begin their talks on normalization in January. However, on Saturday, Castro stressed that Havana will not change its communist system of rule.

"In the same way that we have never demanded that the United States change its political system, we will demand respect for ours," Castro told Cuba's National Assembly, reports Reuters.

Castro also said Cuba faces a "long and difficult struggle" before the United States removes an economic embargo, partly because influential Cuban-American exiles will attempt to "sabotage the process" toward normalization.

On Wednesday, Cuba released U.S. contractor Alan Gross and an instrumental U.S. intelligence agent identified by inside sources as Rolando Sarraff Trujillo. At the same time, the U.S. freed three members of the infamous Cuban Five, who spent more than 15 years in American jails for espionage.

CNN reports that Sarraff is in his early 50s and was convicted of espionage in Cuba in 1995. The office of the director of national intelligence said he provided the U.S. government with information that "was instrumental in the identification and disruption of several Cuban intelligence operatives in the United States and ultimately led to ... successful federal espionage prosecutions."

Sarraff also played a major role in convicting former Defense Intelligence Agency senior analyst Ana Belen Montes. She pleaded guilty of spying for the Cuban government in 2002 and was sentenced to 25 years in prison.

The developments are being hailed as a sweeping diplomatic shift in U.S. policy toward Cuba since 1961 when the embassy closed and the embargo was imposed, following Fidel Castro's takeover of the Cuban government.