Former New Mexico governor Bill Richardson says he will leave Cuba Wednesday after failing to secure the release of an American contractor currently serving a 15-year prison sentence on the island for crimes against the communist state.

Richardson made the comment in Havana Tuesday, after initially saying he would stay in Cuba until he at least had the opportunity to see 62-year-old Alan Gross. Richardson told reporters his conclusion is that perhaps the island's government has decided it does not want to improve ties with the United States. Richardson said he was disappointed at how he was treated on a private visit he said was made at Cuba's invitation.

State Department spokeswoman Victoria Nuland says U.S. officials have been in touch with Richardson and very much regret that he has not been allowed to see Gross. Nuland also said Richardson's trip was not a wasted effort. Last week, the State Department said it was “aware” of the trip and that it supports the former governor's efforts to obtain Gross's release. Nuland did note that Richardson was traveling to Cuba as a private citizen.

Richardson arrived on the Caribbean island last week Wednesday. The former governor, who has often served as a diplomatic troubleshooter in Cuba and North Korea, says freeing Gross is “the key” to improving frosty relations between Washington and Havana.

Richardson visited Cuba a year ago on a similar trip, meeting with Foreign Minister Bruno Rodriguez to discuss Gross's imprisonment. At that time, Richardson said he was told the case against Gross was at a very sensitive investigatory and legal point.

Gross's family has sought his release on humanitarian grounds, saying his health has suffered and that his mother and daughter both have cancer. Last month, Cuba's Supreme Court rejected an appeal from Gross, who was arrested in December 2009 for bringing communications equipment into the country.

At the time of his arrest, Gross was working for a private firm that contracted with the U.S. Agency for International Development. He was accused of distributing Internet equipment and satellite phones to Cuban dissident groups. Gross said he was trying to improve Internet access for the island's small Jewish community and that his actions were not meant to be a threat against Cuba's government.

The United States and Cuba do not have formal diplomatic relations, only interests sections that are technically part of the Swiss embassies in each other's capitals.