Cuban President Raul Castro has warned that Cuba is confronting "ideological and political subversion aimed at toppling its socialist system".
In a speech commemorating the 55th anniversary of the Cuban revolution, Mr Castro said "global power centres" were "subtly introducing neo-liberal and neo-colonial thinking" into Cuba.
But the president said he was confident the country "would emerge victorious".
He was speaking in Santiago, where his brother Fidel declared victory in 1959.
Fidel Castro and his 9,000-strong guerrilla army overthrew US-backed ruler Fulgencio Batista on 1 January 1959.
Fidel Castro went on to lead the country for almost five decades, handing power over to Raul in July 2006 when he became seriously ill.
Raul Castro led the commemorative anniversary gala at Cespedes park in Cuba's second largest city, Santiago - the same spot from where his brother told his supporters in 1959 that the overthrow of Fulgencio Batista had been successful.
"It's been 55 years of constant struggle against the plans of 11 US administrations, that with varying hostility, have not stopped in their goal to change the economic and social regime brought about by the revolution," he said.
Cuba has long blamed the US and the trade embargo it has been enforcing since 1960 for the island's economic woes.
But in Wednesday's speech Mr Castro acknowledged mistakes had been made: "The revolution's programme will be updated every five years so that it can always answer to the true interests of the people and promptly correct any errors."
Mr Castro has been implementing a series of economic reforms since he took over from his brother, including easing regulations on loans, home and car ownership, and loosening travel restrictions.
In December, he shook hands with US President Barack Obama in a gesture which led to speculation as to whether it would signal a thawing of relations between the two foes.
But on Wednesday, Mr Castro defended the revolution, saying it "continues the same, without compromise with anybody, absolute with the people".
Fidel Castro, 87, did not attend the ceremony, but a Spanish newspaper journalist who spoke to him in December said he was "healthy and alert" during the 2.5-hour interview.