Cuba has completed the release of 53 political prisoners that was part of last month’s historic deal between the U.S. and Cuba, the Obama administration said Monday. The move clears a major hurdle for the normalization of ties between the two countries after more than five decades of estrangement.

The prisoners had been on a list of opposition figures whose release was sought as part of the U.S. 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.