The Prime Minister's Office on Tuesday sent a letter to U.S. President Barack Obama requesting the release of convicted spy Jonathan Pollard for humanitarian reasons.

This marked the first formal request by Israel for the release of Pollard.

Pollard was sentenced to life in prison in 1987 on charges of spying on the U.S. for Israel. He is incarcerated at a federal jail in North Carolina.

Prime Minister Benjamin Netanyahu delivered an address to the Knesset on Tuesday evening in which he read the letter.

"Even though Israel was in no way directing its intelligence efforts against the United States, its actions were wrong and wholly unacceptable," Netanyahu wrote in an excerpt from the letter. "Both Mr. Pollard and the Government of Israel have repeatedly expressed remorse for these actions, and Israel will continue to abide by its commitment that such wrongful actions will never be repeated."

The U.S. State Department said on Tuesday that the White House had received the letter and would review it.

The prime minister decided two weeks ago to send a formal letter to Obama calling for Pollard's release.

"I intend to continue to act with determination for the release of Pollard, both because of the State of Israel's moral obligation to him and so that he can live with his family and restore his health after his prolonged incarceration," Netanyahu said in a statement released on December 21.

Netanyahu made the decision to send the letter after meeting with Pollard's wife Esther, as well as Lawrence Korb, who was the U.S. assistant secretary of defense at the time of Pollard's arrest.

After Netanyahu announced his decision to send a letter, State Department Spokesman Philip Crowley responded by saying only that Pollard currently remains in prison.

"Prime Minister Netanyahu has raised this from time to time, both in his current incarnation and in his previous incarnation,' Crowley said, adding that "all I can tell you is Jonathan Pollard remains in prison."