American Jews urged Cuban President Raul Castro on Saturday to release a US contractor "on humanitarian grounds" after the communist island's highest court upheld a 15-year sentence.

In his appeal, Elan Steinberg, vice president of The American Gathering of Jewish Holocaust Survivors & Their Descendants, noted that Alan Gross has lost 90 pounds (40 kilograms) and "is suffering from serious physical ailments as well as from extreme mental stress and anguish."

Gross's daughter and mother-in-law are battling cancer, a point cited by critics of his incarceration.

"Holocaust survivors wish to renew their heartfelt appeal to release Alan Gross from prison on humanitarian grounds and allow him to be reunited with his family in the United States," Steinberg said in a statement.

"We request that President Castro consider Gross's health and family circumstances."

He said that Gross, 62, was an "active and committed" member of the American Jewish community and has "touched and improved the lives of thousands of people" through his humanitarian projects around the world, from the Middle East to Latin America.

Gross was arrested in December 2009 for bringing satellite phones and equipment to Cuba's Jewish community while working as an independent contractor for a democracy-building program funded by the US Agency for International Development.

In its ruling, the Supreme Court's chamber for crimes against the state issued a "final decision" Friday rejecting his appeal, prompting an angry reaction from Washington and fresh calls for the contractor's immediate and unconditional release.

Only Cuba's Council of State, presided by Castro, can now order Gross to be freed.

He had been sentenced to 15 years in prison on March 12 for "endangering the independence and security" of the Cuban state.