Havana, Cuba (CNN) -- Cuba's highest court upheld the 15-year sentence imposed on American contractor Alan Gross for trying to set up illegal Internet connections on the island, state media reported on Friday.
Gross, 62, was jailed in December 2009, when he was working as a subcontractor on a U.S. Agency for International Development project aimed at spreading democracy and deemed illegal by Cuban authorities.
"The Supreme Court ratifies the sentence against U.S. citizen Alan Phillip Gross," according to state-run website Cubadebate.
The Cuban government accused Gross of smuggling satellite equipment into the country to set up an Internet network for dissidents "to promote destabilizing activities and subvert constitutional order."
Gross says he was trying to help connect the Jewish community to the web and was not a threat to the government.
The appeals trial was held last month, although the verdict was only announced on Friday. It was Gross's last legal recourse.
Gross's lawyer said his family was "heartbroken" by the decision.
"Alan and the entire Gross family have paid an enormous personal price in the long-standing political feud between Cuba and the United States," Peter J. Kahn said in a statement.
"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."
The case plunged U.S.-Cuba relations to a new low after signs of thawing when President Barack Obama took office. The State Department has said no progress will be made until Gross is released.
"We deplore the ruling of the Cuban Supreme Court upholding the conviction of imprisoned U.S. citizen Alan Gross," said Mark Toner, acting spokesman at the State Department, in a statement.
Cuba should release Gross "immediately and unconditionally to allow him to return to his family," Toner said.
"The United States remains focused on and concerned about the welfare of Alan Gross. We will continue to use every available diplomatic channel to press for his immediate release," he said.
Former President Jimmy Carter visited Cuba earlier this year and tried to secure the aid worker's release on humanitarian grounds, arguing that Gross's mother and daughter are battling cancer. But he went home empty-handed.
U.S. officials say they hope the Cuban government will consider releasing Gross early now that the courts have had their say.