HAVANA – A Cuban court Saturday found U.S. contractor Alan Gross guilty of crimes against the state and sentenced him to 15 years in prison, a verdict that brought a swift and strongly worded condemnation from Washington.

The court said prosecutors proved that Gross, 61, was working on a “subversive” program paid for by the United States that aimed to bring down Cuba’s revolutionary system. Prosecutors had sought a 20-year jail term.

Tommy Vietor, a spokesman for the White House’s National Security Council, said the ruling “adds another injustice to Alan Gross’ ordeal.”

“He has already spent too many days in detention and should not spend one more,” he said. “We urge the immediate release of Mr. Gross so that he can return home to his wife and family.”

Gross was arrested in December 2009 while on a USAID-backed democracy-building project. The U.S. government and Gross’s family say he was working to improve Internet access for the island’s Jewish community, did nothing wrong, and should be released.

Cuban officials have said the program that Gross worked on showed that the U.S. government continues to seek the overthrow of a Cuban government ruled since 1959 by brothers Fidel and Raul Castro.