Roberto León / NBC News

Josefina Vidal, Cuba's director of U.S. Affairs at the Ministry of Foreign Affairs, addresses the media in Havana on Wednesday.

HAVANA -- A Cuban official on Wednesday accused the U.S. government of “lying” about the health of Alan Gross, an American contractor serving a 15-year prison sentence here, in an effort to force his release. 

Denying speculation that the 63-year-old Gross has cancer or is otherwise in poor health, Foreign Ministry official Josefina Vidal said at a press conference in the Cuban capital that the 63-year-old American has "been treated decently and well in prison.”

She also stated that “his health has "not deteriorated" and that he "speaks regularly with friends and family."

"Gross has been seen by the most qualified Cuban medical specialists," Vidal said. "The U.S. government is lying to suggest that he has cancer and that he is not receiving adequate treatment." If these lies continue, she said, "Cuba will present new evidence that shows Gross is not sick."

Vidal’s statement came in response to increasing pressure from the U.S. government and lawmakers to release Gross, who was convicted in 2009 of "acts against the independence and/or territorial integrity of the state” for  distributing telecommunications equipment to Cuba’s tiny Jewish community.

At the time, Gross was in Cuba on a  tourist visa, working  for Development Alternatives, Inc., a State Department contractor, as an "independent business and economic development consultant" under an $8.6 million contract from the U.S. Agency for International Development.

The court that convicted him described the effort as an effort to subvert the Cuban government.

“It was demonstrated that (Gross) illegally introduced telecommunications equipment in Cuba to create internal networks as part of a program of the government of the United States that aimed to promote destabilizing actions in the country and subvert Cuban constitutional order," it said at the time.

Since his imprisonment more than three years ago, Gross has lost more than 100 pounds and developed a mass on his right shoulder blade, which Cuban doctors diagnosed as a non-malignant hematoma that would be reabsorbed within a few months, according to Reuters.

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Gross’ wife, Judy, has been leading a public relations campaign in the United States for her husband’s release on humanitarian grounds. An American radiologist she consulted said last month that the mass had not been properly evaluated and speculated that it could be cancerous. The radiologist, Alan Cohen, said that Gross needed an urgent evaluation – and likely a biopsy of the mass – preferably at a facility in the United States.

At a press conference on Capitol Hill Tuesday – the fourth anniversary of her husband’s imprisonment – Judy Gross said her husband “is frail, suffers from chronic pain ... and still doesn’t know whether he has cancer.”

U.S. State Department spokesman Mark Toner sounded a similar theme on Monday.

“Mr. Gross has lost more than 100 pounds and suffers from severe degenerative arthritis that affects his mobility, and other health problems,” he said in a statement. “His family is anxious to evaluate whether he is receiving appropriate medical treatment, something that can best be determined by having a doctor of his own choosing examine him.”

While resisting calls to release Gross, Cuban officials have floated an alternative to resolve the impasse: They say they will free Gross if President Barack Obama agrees to release five Cuban spies held in the U.S.

The spies – known as the Cuban Five – are national heroes in Cuba as a result of their mission in the late 1990s to infiltrate  anti-Castro exile groups in South Florida that Havana suspected of plotting terrorist attacks inside Cuba. They were convicted in Miami in June 2001 of conspiracy to commit espionage, conspiracy to commit murder, acting as an agent of a foreign government, and other illegal activities.

Vidal referred to this scenario on Tuesday, reiterating “Cuba's willingness to immediately start talks with the U.S. government to find a humanitarian solution that is mutually beneficial to both parties." She also stated that her government would not make a "unilateral" move and release Gross because the "problem also belongs to the U.S." -- referring to the Cuban Five.

Gross himself pushed for a diplomatic solution in a meeting on Nov. 28 with Peter Kornbluh, a Cuba specialist from the National Security Archives in Washington.

"He’s angry, he’s frustrated, he’s dejected — and he wants his own government to step up" and negotiate, Kornbluh told NBC News last week. "His message is that the United States and Cuba have to sit down and have a dialogue without preconditions. … He told me that the first meeting should result in a non-belligerency pact being signed between the United States and Cuba."

Mary Murray is an NBC News producer; NBC National Investigative Correspondent Michael Isikoff also contributed to this report.

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