The official, who was traveling with US Secretary of State John Kerry, spoke on condition of anonymity because the official was not authorized to discuss the issue on the record.
The official said the US has verified the release of the prisoners.
The prisoners had been on a list of opposition figures whose release was sought as part of the US agreement last month with the Cuban government.
They had been cited by various human rights organizations as being imprisoned by the Cuban government for exercising internationally protected freedoms or for their promotion of political and social reforms in Cuba, AP reported.