(Adds comments by supporter of Cuban Five, background)
By Zachary Fagenson
MIAMI, Jan 29 (Reuters) - A Cuban intelligence agent jailed for 15 years for spying on Cuban American exiles in Miami is due to be freed next month, but may have to remain in the United States for three years of supervised release, according to the Federal Bureau of Prisons.
Fernando Gonzalez, 50, was arrested by the FBI in 1998 along with four other Cuban agents who were convicted in 2001 of 26 counts of spying on behalf of Fidel Castro's government.
The case of the "Cuban Five" is widely considered an impediment to improving the hostile relations between the United States and Cuba, separated by only 90 miles (145 km) of sea.
Gonzalez, who also goes by Ruben Campa, was sentenced to 19 years, which was reduced on appeal in 2008 due to good behavior.
He is due to be released on Feb. 27 from a jail in Arizona and moved to an immigration facility, according to Gloria La Riva, coordinator for the National Committee to Free the Cuban Five which is campaigning for their freedom.
"We are hopeful that he will be able to go home soon after," she said. "The lawyers are negotiating with the immigration authorities to let that happen," she added.
A lawyer for Gonzalez declined to comment. U.S. immigration officials did not immediately respond to a phone call asking about Gonzalez's possible return to Cuba.
Another agent, Rene Gonzalez, was released in 2011 after serving more than 13 years and now lives in Cuba. Gonzalez was allowed to return to Cuba rather than serve out a three-year parole in Florida but only after he agreed to renounce his U.S. citizenship.
The group, called La Red Avispa or the Wasp Network, infiltrated a Miami-based activist group, Brothers to the Rescue, and attempted to spy on U.S. military installations without much success, relaying coded messages back to Havana.
Cuba considers the agents national heroes, arguing they were unjustly convicted and were mainly collecting information on Cuban exile groups it accuses of planning guerrilla actions against the island.
The trial was held in Miami, center of the Cuban exile community and hotbed of opposition to Cuba's communist government.
One agent, Gerardo Hernandez, is serving a double life sentence after being convicted of involvement in the shooting down of two small U.S. planes off the Cuban coast in 1996. Four people aboard the planes were killed flying a Brothers to the Rescue mission looking for Cubans trying to cross the Florida Straits in flimsy home-made rafts.
Cuba accused the planes of violating Cuban air space.
The two other agents still in jail, Antonio Guerrero and Ramon Labanino, also had their sentences reduced. Guerrero is serving 21 years and 10 months and is due for release in September 2017, while Labanino is serving 30 years and is due for release in October 2024.
The agents' case snarled already hostile U.S.-Cuba relations and gained greater attention after the arrest of U.S. contractor Allen Gross in Havana in 2009. Cuba sentenced Gross to 15 years in jail for his role in a U.S. government effort to set up an underground Internet network on the Caribbean island.
The U.S. has demanded that Gross be freed, while Cuba has hinted it might consider a deal to release him if Washington lets the Cuban Five out of jail in exchange. The Obama administration has repeatedly said it will not consider an exchange. (Editing by David Adams, Stephen Powell and Cynthia Osterman)