A U.S. government contractor jailed for four years in Cuba appealed to President Barack Obama on Tuesday to take any steps necessary to secure his release.
"Why am I still here? 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," Alan Gross wrote in a letter to Obama.
White House spokesman Jay Carney said Obama had "personally engaged foreign leaders and other international figures to use their influence with Cuba" to have Gross freed, adding that the administration renewed its call for his release.
Gross' letter was read aloud by his wife at a vigil in Lafayette Square across from the White House on Tuesday to mark his fourth anniversary in jail.
"It is clear to me, Mr. President, that only with your personal involvement can my release be secured," Gross wrote.
Tuesday's vigil signaled a change of tactic by the Gross family, which has previously steered clear of asking Obama to negotiate with Cuba, preferring instead to demand his unconditional release.
Gross, 64, of Potomac, Maryland, was arrested in Havana on December 3, 2009, for his work on a semi-covert U.S. program promoting political change on the island. Cuba has said it considered the work to be subversive.
Gross said he was in Cuba to set up communications equipment to give unrestricted Internet access to Jewish groups. A Cuban judge said that activity was a crime against the state and sentenced Gross to 15 years.
"There has to be dialogue (with Cuba)," Gross' wife, Judy, told Reuters. "If we carry on treating it the way we have been I think that's a death sentence for Alan. He'll die in jail. President Obama needs to make it his personal crusade."
Cuba had agreed to sit down with U.S. government officials, without conditions, she said, to discuss possible terms leading to her husband's release and return home. But the State Department has rejected any negotiated settlement of the case out of hand.
In other cases of Americans jailed abroad, including North Korea, the United States has appointed a special envoy to negotiate, Judy Gross said. That has not happened in Alan Gross' case, she said, nor has Obama responded to repeated letters from the family requesting a meeting.
A representative of the Gross family said more than 100 people attended Tuesday's vigil.
Last month Obama was sent a letter by a bipartisan group of 66 senators, led by Patrick Leahy, a senior Democrat, that urged the president "to act expeditiously to take whatever steps are in the national interest to obtain his release."
A separate letter signed by 14 senators, including two of Cuban descent, Robert Menendez of New Jersey and Marco Rubio of Florida, took a tougher line rejecting any negotiations, calling on Obama to work toward securing Gross's unconditional release.
"Rather than simply demanding his release - which has achieved nothing in four years - the administration needs to act, as it has in cases of other Americans imprisoned overseas, to bring Alan home to his wife Judy and his family," Leahy, the Senate's most senior member, said in a statement on Tuesday.
Tuesday's vigil was attended by 75 Jewish leaders politicians, family and friends.
Gross has lost more than 100 pounds in jail, suffers from chronic arthritis, and his mental health is deteriorating, according to his family. "He's gone from a happy go-lucky, gregarious person, to very down and depressed," said his wife.
But a visit this summer by independent doctors had reassured the family he was not suffering from cancer after a growth was detected on his shoulder.
The U.S. State Department also marked the anniversary by calling for the immediate release of Gross saying his continued captivity on the communist-ruled island was "gravely disappointing."
The Gross case has become a major obstacle to improved U.S. relations with Cuba after more than 50 years of hostility.
It remains unclear what steps the Obama administration can take to obtain Gross's release. Cuba has hinted it would release him in return for four Cubans jailed on espionage charges in the United States, but Washington has flatly ruled that out.
Other options might include an apology issued by the Obama administration to Cuba for sponsoring Gross' activities in violation of Cuban law, or some relaxation of U.S. economic restrictions on trade between the two countries such as removal of Cuba from the U.S. list of state sponsors of terrorism.
(Additional reporting by Steve Holland in Washington; Editing by Bill Trott)