Image copyright AP Image caption Jonathan Pollard was jailed for life in 1987 for passing thousands of classified documents to Israel

Discussions are "under way" on the potential release of Jonathan Pollard, an American imprisoned for spying for Israel, the White House has said.

His release in an effort to save stalled Middle East peace talks would require Israel to make big concessions to the Palestinians in return.

Pollard, a former US Navy intelligence analyst, was imprisoned for life in 1987 for passing documents to Israel.

US Secretary of State John Kerry has flown to the region for urgent talks.

"Jonathan Pollard was convicted of espionage and he is serving his sentence," White House spokesman Jay Carney said on Tuesday.

"There are obviously a lot of things happening in that arena and I am not going to get ahead of discussions that are under way,"

A US official earlier told the New York Times no decisions had yet been made on Pollard's release, but confirmed discussions had taken place on the matter.

Analysis The rules of engagement for the peace talks between Israel and the Palestinians were clear - no leaks, briefings or tip-offs while negotiations went on in secret. But there's an unmistakeable air of desperation to John Kerry's shuttle diplomacy that suggests the talks are closer to breakdown than breakthrough. Having embarked on the process in the personal belief that a historic deal was possible the US secretary of state now finds himself scrambling to broker a compromise just to keep the two sides talking beyond the current deadline. The basic elements of a deal are widely discussed in Israel and on the West Bank - although without any confirmation from official sources. In return for a Palestinian agreement not to proceed with grievances against Israel at global bodies like the International Criminal Court, the Israeli government would complete a current round of releases of Palestinian prisoners and agree to more. Some sort of partial construction freeze in Israeli settlements on the West Bank might also be included. To sweeten those concessions for Israel the United States might then free Jonathan Pollard - an American official who spied for the Israelis in the 1980s. So there are a lot of cards on the table - the problem for John Kerry is that they have to be played not to bring the talks to a successful conclusion but to keep them going at all.

Mr Kerry is said to have held two meetings with Israeli Prime Minister Benjamin Netanyahu on Monday, and had discussions with chief Palestinian negotiator Saeb Erekat, before flying out after only several hours.

None of the sides have commented on the talks.

It is the second time that Mr Kerry has interrupted his schedule to press Israel and the Palestinians to extend the direct peace talks beyond 29 April - the deadline set last summer when they resumed after a three-year hiatus.

His plan has been derailed by a dispute over the release of a fourth batch of 26 long-term Palestinian prisoners from Israeli jails.

Mr Abbas had insisted that they be freed by 29 March, in keeping with a promise made by Israel before the direct negotiations resumed.

Israeli officials have said they are reluctant to proceed unless the Palestinians commit to extending the talks, and stressed that the releases have always been tied to their progress.

The previous three releases were deeply unpopular with the Israeli public because many of the prisoners were convicted of murdering Israelis.

The possible release of Pollard has reportedly emerged as an incentive for Israeli co-operation.

Like his predecessors, Mr Obama has refused to release the 59-year-old despite repeated pleas from Israeli leaders.

However, last year he told Israeli TV that he would make sure his sentence would be "accorded the same kinds of review" as every other American prisoner.

Image copyright Reuters Image caption Kerry's latest visit was unscheduled and at a time when the talks hang in the balance

Officials familiar with the negotiations told the New York Times that Pollard's possible release was one element in discussions about a broader arrangement that had not yet been reached and that the president would need to approve.

Two people close to the talks told the Associated Press that in return for such a move, Israel would have to undertake significant concessions to the Palestinians.

Concessions could include some kind of construction freeze at Jewish settlements on occupied territory, the release of further batches of Palestinian prisoners, and a guarantee not to pull out of the talks.

Israel's government has also not commented, but senior Israeli sources told the Maariv newspaper that the "Pollard issue is on the table".