HAVANA – Cuba’s Supreme Court has upheld the 15-year prison sentence of jailed American aid contractor Alan Gross for trying to set up Internet networks in Cuba, in a damaging decision for U.S.-Cuba relations.

The Cuban government said on Friday the court upheld the finding in his March trial that he illegally took equipment into Cuba to spread Internet access under a U.S. program “to subvert the Cuban constitutional order.”

The case has brought U.S.-Cuba relations to a standstill after a brief warming under President Barack Obama, who eased U.S. travel restrictions to Cuba and allowed a free flow of remittances to the island before Gross, 62, was arrested in December 2009.

The Obama administration has said there would be no more improvement in U.S.-Cuba relations as long as Cuba imprisons Gross, who has been behind bars for 20 months, and called for him to be “immediately and unconditionally” released.

“We deplore the ruling of the Cuban Supreme Court,” said U.S. State Department spokesman Mark Toner. “We will continue to use every available diplomatic channel to press for his release.”

The court’s decision followed a July 22 appeal to the Supreme Court that was Gross’ last legal recourse in the case.

The outcome was not a major surprise, although some had expected the court to at least reduce his sentence.

The court rejected Gross’ defense that he intended no harm toward Cuba and was only trying to provide more Internet access to the island’s small Jewish community.

He was working for a secretive U.S. Agency for International Development program that Cuba views as part of longstanding U.S. efforts to destabilize the island’s government. It considers the Internet one of the new battlegrounds in the two countries’ half-century old ideological conflict.

The program has drawn criticism in Washington for ineffectiveness and for putting Gross, who had engaged in development projects around the world, in danger.