Alan Gross, the U.S. government subcontractor serving a 15-year sentence in Cuba after being convicted of subversion, has asked President Barack Obama to "take whatever steps are necessary" to bring him home.

"With the utmost respect, Mr. President, I fear that my government - the very government I was serving when I began this nightmare - has abandoned me," the 64-year-old Maryland man said in a letter to the president.

The missive was sent via the U.S. Interests Section in Havana and is to be delivered to the White House on Tuesday, the fourth anniversary of Gross' arrest in Cuba.

"It is clear to me, Mr. President, that only with your personal involvement can my release be secured," Gross said in the letter, a copy of which was provided to the Washington Post.

The letter comes a month after a bipartisan group of 66 senators, headed by Vermont Democrat Patrick Leahy, urged in another missive to Obama that he "act expeditiously to take whatever steps are in the national interest to obtain (Gross') release."

Since 2009, the Obama administration has been asking Cuba publicly and privately to release Gross.

In a statement, the State Department once again on Monday demanded his "immediate and unconditional" release.

"I know that your administration and prior administrations have taken extraordinary steps to obtain the release of other U.S. citizens imprisoned abroad - even citizens who were not arrested for their work," Gross said in his message to Obama.

Gross' wife Judy is planning to participate in a demonstration on Tuesday in front of the White House on the fourth anniversary of her husband's arrest.

Gross traveled to Cuba on behalf of a Maryland company that won a contract from the U.S. Agency for International Development to expand Internet access and the flow of information on the Communist-ruled island.

He was arrested in Cuba in December 2009 with satellite communications equipment in his possession. Havana said he was illegally aiding dissidents and inciting subversion.

In August 2012, Cuba's highest court upheld the 15-year jail sentence imposed on the American.

Cuba has hinted that it would release Gross in exchange for the return of the four members of the "Cuban Five" intelligence agents who remain jailed in the United States.

Washington dismisses talk of a possible swap. EFE