By Marc Frank
HAVANA (Reuters) - Cuba held a day of protest on Thursday over four intelligence agents imprisoned in the United States, displaying yellow ribbons to show national support for bringing the men home on the 15th anniversary of their arrest in Florida.
It was the largest anti-U.S. protest staged in the communist country since President Raul Castro took over from his ailing brother Fidel in 2006.
The men were convicted in 2001 of conspiring to spy on Cuban exile groups and U.S. military activities as part of an espionage ring called the "Wasp Network."
A fifth Cuban agent, Rene Gonzalez, who was released two years ago and now lives in Cuba, headed the public drive for the return of his colleagues, who are considered national heroes at home and are known in the United States as the "Cuban Five".
Raul Castro took part in a televised cultural event in their honour on Wednesday evening and a concert with top Cuban performers was scheduled on Thursday in front of the U.S. Interests Section in Havana.
Many of the country's 11.2 million residents joined the protest, according to sources in different cities. Yellow ribbons hung from trees, lamp posts and car antennas from Havana to Camaguey city in central Cuba and eastern Santiago.
The Chicago-born Gonzalez, 57, who returned to Cuba this year after renouncing his U.S. citizenship, said in a televised address last week that yellow ribbons, symbolizing longing for absent loved ones, were meant to resonate with the "average American."
The United States and Cuba do not have diplomatic relations but have lower level interests sections in each other's capital.
The agents' case has dogged the already-hostile U.S.-Cuba relations and gained greater attention after the 2009 arrest of U.S. contractor Allen Gross in Cuba. He was sentenced to 15 years for his role in a U.S. government effort to set up an underground Internet network on the Caribbean island.
Havana has linked the fate of its agents with that of Gross, stating a humanitarian solution is needed for both cases.
Cuba says its agents were unjustly convicted and says they were mainly collecting information on Cuban exile groups planning violent actions against Cuba.
One agent, Gerardo Hernandez, is serving a double life sentence after being convicted of involvement in the shooting down of two U.S. planes in 1996 flown by an exile group that dropped anti-government leaflets over Havana. He denied the charge.
The other three are serving sentences ranging from 18 years to 30 years.
(Editing by David Adams and David Storey)