The court on Saturday sentenced Gross, 61, of Maryland to 15 years in prison from crimes against the state. The State Department has described Gross as a U.S. contractor assisting Cuba's Jewish community.
"Today's sentencing adds another injustice to Alan Gross's ordeal," Tommy Vietor, the U.S. National Security Council spokesman said in a statement. "He has already spent too many days in detention and should not spend one more. We urge the immediate release of Mr. Gross so that he can return home to his wife and family."
Gross, 61, was detained in December 2009 as he prepared to return to the United States from Cuba.
The U.S. Agency for International Development says Gross was a contractor who was bringing Internet access to the island's small Jewish community. Gross had conducted similar projects in other developing countries, but the main Jewish groups in Cuba have denied any contact with or knowledge of Gross or the program.
Jewish groups and public figures, including Rev. Jesse Jackson, have appealed for his release on humanitarian grounds. Gross, who suffers from grout, is ailing and his mother and daughter are both being treated for cancer.
"Having already served a 15-month sentence in a Cuban prison, Alan and his family have paid an enormous personal price in the long-standing political feud between Cuba and the United States," Gross' U.S. lawyer, Peter Kahn, said in a statement. "We will continue to work with Alan’s Cuban attorney in exploring any and all options available to him, including the possibility of an appeal."