* Continued Israeli-Palestinian negotiations in doubt
* Arab leaders back Abbas's balking on "Jewish state" (Adds State Department briefing, background, Kerry-Abbas meeting starts, paragraphs 4, 6-9)
By Lesley Wroughton
AMMAN, March 26 (Reuters) - U.S. Secretary of State John Kerry broke from a visit to Italy on Wednesday to try to salvage Israeli-Palestinian peace talks, even as Arab leaders declared they would never meet Israel's core demand to be recognised as a Jewish state.
Kerry flew to Jordan to ask Palestinian President Mahmoud Abbas to commit to extending the negotiations, just days before Israel is supposed to release a final group of Palestinian prisoners as a confidence-building gesture.
Before it releases the prisoners, Israel wants to be assured Abbas won't abandon the U.S.-brokered talks, which resumed last July after a three-year break. Having initially set next month as the target date for a peace accord, Kerry is now trying to get the sides to a agree a framework for further negotiations.
Kerry began his meeting with Abbas late on Wednesday.
Kerry began his visit to Amman by meeting Jordan's King Abdullah, another Israeli-Palestinian mediator. He also spoke by telephone with Israeli Prime Minister Benjamin Netanyahu during the three-hour flight from Rome, U.S. officials said.
The two were due to speak again after Kerry dined with Abbas.
Israel's Army Radio said Washington had offered to free Jonathan Pollard, a former U.S. Navy intelligence analyst who was sentenced to a life term in 1987 in the United States for spying for Israel, if Israel went ahead with the prisoner release, keeping Abbas on the diplomatic track.
At a briefing in Washington, State Department spokeswoman Marie Harf said, "There are no plans to release Jonathan Pollard at this time."
But when asked to state unequivocally that Pollard's imprisonment is not part of the current negotiations, Harf sidestepped the question by saying, "Look, I'm not going to get into any specifics confirming or not confirming one way or the other if any topic is on the table in these talks."
A succession of U.S. presidents have spurned Israeli calls for Pollard's pardon. Netanyahu, commenting in December in the aftermath of reports that the United States had spied on Israel's leaders, said at that time that Israel had constantly sought Pollard's release.
State Department spokeswoman Jen Psaki said Kerry wanted to "narrow the gaps between the parties."
ISRAELI ARABS ON PRISONER ROSTER
The Palestinian Prisoners Club, the main group looking after the welfare of Palestinians jailed by Israel, said there were 30 prisoners due to be freed by Israel on March 29. They include 14 Arab citizens of Israel.
U.S. officials have long cautioned that the release of the last batch of prisoners will be difficult and have been given no assurance by Israel that it will go ahead.
Further complicating Kerry's 11th-hour diplomatic push was a statement on Wednesday by Arab leaders that they will never recognise Israel as a Jewish state.
The statement at the end of a two-day Arab League summit in Kuwait also denounced the continued building of Jewish settlements in the occupied West Bank, on territory where Palestinians seek statehood.
"We hold Israel entirely responsible for the lack of progress in the peace process and continuing tension in the Middle East," the statement said. "We express our absolute and decisive rejection to recognising Israel as a Jewish state."
Israel says Palestinian refusal to recognise it as a Jewish state is the main stumbling block in the peace talks.
Abbas' refusal "to discuss mutual recognition between two nation state stands in stark contrast with Prime Minister Netanyahu's willingness to recognise a Palestinian state and his agreement that all of the core issues can be raised in the talks," a senior Israeli official told Reuters.
U.S. President Barack Obama has repeatedly declared his vision of peace - a Jewish state of Israel and a state of Palestine living side by side in peace in security. He recently called on Abbas to take risks for peace with Israel.
Abbas has argued that the Palestinians already acknowledged Israel's right to exist in 1993.
Palestinians fear recognising Israel as a Jewish state would prejudge the demand of refugees from the 1948 war of its founding to return. Israel has ruled out any such influx, saying the refugees should resettle in a future Palestinian state. (Additional reporting by Will Dunham in Washington; Editing by Tom Heneghan)