The Cuban agents were imprisoned for more than a decade for spying. Castro told that these agents are known as 'Five Heroes' in Cuba.
The five men were arrested in 1998 and convicted in a Miami court in 2001 of 26 counts of spying. They received sentences ranging from 15 years to life in prison.
US claimed that the men were part of a Cuban espionage ring that spied on the Cuban exile community in Florida and sought to penetrate US military facilities.
Castro also told that one of the Cuban agents was placed in a tiny cell with another prisoner.
"There are two men in a space one meter in width. He is not only in a high-security prison, which is already a deep hole, he is in a hole inside the hole," said Castro.