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Israel is ratcheting up calls on Washington to release convicted spy Jonathan Pollard, in a campaign that has reopened a long-running feud with its closest and most important ally.

Israeli leaders say that after 27 years the former civilian intelligence analyst for the U.S. Navy should be freed. But the White House is standing firm, rejecting Israeli appeals based in part on claims that Pollard suffers from life-threatening ailments.

Pollard, 57, was arrested by FBI agents in Washington in 1985 after unsuccessfully seeking refuge at the Israeli Embassy in Washington. He pleaded guilty to leaking classified documents to Israel and received a life sentence. He is eligible for parole in three years.

Pollard, who is Jewish, enjoys widespread sympathy in Israel, where many believe the sentence was too harsh and where he was granted citizenship after he was imprisoned.

The Pollard affair is enmeshed in a web of highly fraught issues. One is the very idea of spying against an ally — especially a country's primary patron. Another is the delicate issue of suspected dual loyalties among American Jews, and their own concerns about being seen in such a light.

Then there is the mostly unspoken, yet frequently assumed, question of linkage — namely that the U.S. would reward Israel for progress made in peace efforts with the Palestinians with Pollard's release. On that score the prospects seem especially dim: President Barack Obama and Israeli Prime Minister Benjamin Netanyahu have clashed repeatedly over Israeli policy, especially settlement construction in the West Bank.

The Pollard issue took on new life this week after his wife, Esther, said he had been hospitalized in extreme pain. In an emotional meeting with President Shimon Peres, she said she did not want to become a widow.

Pollard's lawyer, Nitzana Darshan-Leitner, said he suffers from diabetes, high blood pressure and kidney stones.

Peres, a Nobel Peace laureate, responded by appealing to Obama to release Pollard as a humanitarian gesture.

The Israeli president's office refused to release the letter, but officials said it noted the dramatic deterioration in Pollard's health, Peres' belief that Pollard does not pose a security threat at this point and the strong ties between Israel and the United States.

The White House issued a statement Tuesday saying American policy on the issue hasn't changed, but Israeli officials said no formal response had been received from Obama.

Peres is set to meet Obama at the White House in June, when he is to receive the Presidential Medal of Freedom, the highest civilian award in the United States. That has animated hopes that Peres — a globally respected elder statesman who has far better ties with Obama than Netanyahu — might use the occasion and press the issue. More than 24,000 Israelis have joined a Facebook page urging Peres to skip the event if Pollard is not freed.

Netanyahu, who made a private visit to Pollard in prison a decade ago, has repeatedly raised the issue in his periodic meetings with Obama.

Noting Jews are celebrating Passover — a holiday marking the ancient Israelites' freeing from Egyptian bondage — Netanyahu said earlier this week that "the time has come" to release Pollard. "We must let him finish his life in dignity," he said.

Israel has made similar appeals in the past, most recently when it unsuccessfully urged American officials to allow Pollard to leave prison to attend his father's funeral in Indiana.

But the sense of urgency has grown due to concerns about his health.

Ronit Tirosh, an Israeli lawmaker who heads a parliamentary caucus pressing for Pollard's release, said that with time running out, Israel has to be vocal in its appeals, even if it upsets its American allies.

"He's so sick, and so many years have passed, we have nothing to lose," she said. She described Peres' appeal as "the last card we have" with the Americans.

Tirosh and many other Israelis argue that the punishment has been excessive, and that many other Americans convicted in espionage have served lesser sentences.

Netanyahu himself attempted to link the Pollard issue to peacemaking during his first term as prime minister, pressing for Pollard's release as part of a 1998 interim deal with the Palestinians. President Bill Clinton, who was hugely popular in Israel, rejected the request after fierce opposition from U.S. intelligence officials.

Deputy Prime Minister Danny Ayalon, a former ambassador to Washington, was quoted in the Israeli daily Yediot Ahronot Wednesday as saying American officials had told him they were convinced Pollard had an accomplice. The paper quoted Ayalon as saying the Americans had offered to release Pollard in exchange for the name of the accomplice — but Ayalon insisted Pollard had worked alone. Ayalon did not respond to an interview request.

Even after more than a quarter of a century, many details of the case remain a mystery. Pollard delivered hordes of documents to his handlers, and the full extent of what was released has never been revealed.

Darshan-Leitner, Pollard's lawyer, said the information was material that had traditionally been shared with the Israelis. She said the information had included details about Arab and Soviet military capabilities, and had helped Israel carry out the assassination of a senior PLO official in Tunisia in 1988.

Much of the American military and intelligence community remains opposed to releasing Pollard.

But this opposition has begun to crack, raising hopes that a breakthrough may finally be near. Former secretaries of state Henry Kissinger and George Schultz, Lawrence Korb, the assistant secretary of defense at the time, former CIA Director R. James Woolsey, Sen. John McCain and former Vice President Dan Quayle have all called for Pollard's release in recent years.