A U.S. citizen whose arrest and jailing by the Cuban government has been a source of friction between the island nation and the United States has lost his last appeal to be set free.

Cuba's Supreme Court on Friday rejected the appeal by Alan Gross, a U.S. government subcontractor, challenging his 15-year prison sentence for crimes against the state.

Gross' request to have his sentence reduced or thrown out was denied in a "definitive resolution," a note on state-run website Cubadebate said.

Gross has been behind bars since his arrest in December 2009, and this spring he was found guilty of bringing satellite and other communication equipment into the country illegally.

The Maryland native has acknowledged he was working on a USAID-funded democracy program, but says he meant no harm to the government.

"While we are not surprised, we are extremely disappointed with today's ruling, which marks the end of Alan's legal process in Cuba," Gross' U.S. lawyer, Peter J. Kahn, said in a statement. "The family is heartbroken by today's decision, but remains hopeful that there continues to be room for a diplomatic resolution of this matter."

The Cuban high court's ruling brought immediate condemnation from Florida's U.S. Sen. Marco Rubio, a Cuban-American. 

“This is a deplorable human rights violation," Rubio said in a statement. "It has been well documented that Mr. Gross is simply a humanitarian who was seeking to help the Jewish community in Cuba access the Internet."

"The Castro regime’s cowardly fear of what would happen if Cuban citizens have access to uncensored information does not justify this man’s incarceration at all, much less for 15 years," Rubio said. "Mr. Gross’ unjust sentence is the latest example of everything that is wrong with the Castro regime.  For every Alan Gross, there are many more Cubans being incarcerated, harassed and repressed for simply yearning to be free."  

U.S. officials have said they did not expect the court to throw out Gross' conviction, but have held out hope that the end of the legal process might clear the way for his release on humanitarian grounds. Gross, 62, has lost 100 pounds (45 kilograms) in jail by his own estimation, and several family members in the United States have serious illnesses.

Cuban officials have said privately they are sympathetic to humanitarian appeals, but would not consider them until the Supreme Court ruled.

"Entering his 21st month in a Cuban prison, Alan and the entire Gross family have paid an enormous personal price in the long-standing political feud between Cuba and the United States," Kahn's statement continued. 

"Now, more than ever, we call upon the two countries to resolve their dispute over Alan's activities diplomatically, and request that President Raul Castro release Alan immediately on humanitarian grounds."

This is based on a story by The Associated Press.

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