Former New Mexico Gov. Bill Richardson said here Tuesday that he is leaving Cuba "very disappointed" after the island's Communist government refused to let him meet with a U.S. aid contractor sentenced to 15 years in prison for subversion.

"I have been here a week and tried through all means - with religious institutions, diplomats from other countries, all kinds of efforts - and I see that this isn't going to change," he said at a press conference in Havana. "So why would I stay?"

Richardson, who vowed last week to remain on the island until authorities allowed him to visit Alan Gross at the Havana military hospital where he is being treated for an unspecified health problem, said he will leave Cuba on Wednesday.

"Perhaps the Cuban government has decided it does not want to improve relations. Perhaps that is the message it is sending," the former governor, lawmaker, ambassador and Cabinet secretary said.

Noting his years of advocating for better U.S.-Cuba ties, Richardson said he was "very disappointed and surprised" by Cuban officials' unwillingness to let him see Gross or even to discuss the case.

Though here as a private citizen, Richardson's efforts had the blessing of the U.S. State Department, which also expressed regret Tuesday at the apparent failure of the mission.

This is the second time Richardson has traveled to Havana in a bid to secure the release of the 62-year-old Gross, while former President Jimmy Carter made a similar attempt six months ago.

Gross, a sub-contractor for the U.S. Agency for International Development, was arrested Dec. 3, 2009, in possession of satellite communications equipment he said he was planning to distribute among Cuba's Jewish community.

Havana says he was illegally aiding dissidents and inciting subversion on the Communist-ruled island.

Last month, Cuba's highest court upheld the 15-year jail sentence imposed on Gross in March.

The case has increased friction between Cuba and the United States, which have not had diplomatic relations since 1961, though each country maintains an interests section in the other's capital.

Gross has lost around 45 kilos (100 pounds) while in custody and is ailing and depressed, Richardson said Tuesday, stressing the "humanitarian element" of the affair.

While here, Richardson met with Cuban Foreign Minister Bruno Rodríguez and with the island's Catholic primate, Cardinal Jaime Ortega.

The governor said that though Rodríguez raised the issue of the five Cuban spies held in U.S. prisons, there was no discussion of exchanging Gross for the intelligence officers.

Follow us on twitter.com/foxnewslatino
Like us at facebook.com/foxnewslatino