Cuba’s top court has rejected the final appeal of a U.S. government contractor sentenced to 15 years in prison, despite appeals from top American officials for his release.

(Courtesy Sharon J. Castillo)

Gross’s attorneys had petitioned Cuba’s Supreme Court to reduce or dismiss the sentence, and the State Department called Gross’s continued detention an obstacle to improved relations between Cuba and the United States. Still, the court denied Gross’s appeal in a “definitive resolution,” according to an article posted Friday to the state-run Web site Cubadebate.

“While we are not surprised, we are extremely disappointed with today’s ruling, which marks the end of Alan’s legal process in Cuba,” Peter J. Kahn, an attorney for Gross, 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.”

At the time of his arrest, Gross was working for a Bethesda firm, Development Alternatives, which had won a $6 million U.S. government contract to promote democracy in Cuba. His work included the distribution of satellite phone equipment and computer gear to members of Cuba’s Jewish community. He lacked a permit, which is required under Cuban law.

U.S. officials have defended the program, saying it was aimed at helping Cubans communicate with others around the world. On Friday, the White House again urged Cuba to free Gross “immediately and unconditionally.”

Gross’s family has called for his release on humanitarian grounds. After 21 months in prison, the 62-year-old has lost about 100 pounds from his original 250; one his daughters is battling cancer.

“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, the lawyer, said. “Now, more than ever, we call upon the two countries to resolve their dispute over Alan’s activities diplomatically, and request that President Raúl Castro release Alan immediately on humanitarian grounds.”