US Secretary of State John Kerry vowed on Sunday that any Israeli-Palestinian peace agreement would improve the security of both sides and would be "fair and balanced," as he was preparing on Sunday morning to depart from his latest round of shuttle diplomacy.

"I can guarantee all parties that President (Barack) Obama and I are committed to putting forward ideas that are fair and balanced, and to improving the security of all peoples," AFP quote him as telling journalist in Jerusalem.

Speaking before he flew to Jordan and Saudi Arabia to brief their rulers on the talks, Kerry said both sides had a sharper idea of the compromises needed to secure an agreement despite their deep skepticism on the chances of success.

He noted that while progress was being made in the talks, there was still a chance no accord would be reached.

Kerry was slated to return to Israel Sunday night at 9 p.m. and conduct further talks with Prime Minister Binyamin Netanyahu on Monday.

"This has been a productive couple of days," Kerry told reporters after three days of separate talks with Netanyahu and Palestinian Authority President Mahmoud Abbas. "We have had very positive - but I have to say very serious, very intensive - conversations."

Kerry said all of the major issues in the conflict - borders, security, the fate of Palestinian refugees and the status of Jerusalem - were under discussion.

"The path is becoming clearer. The puzzle is becoming more defined. And it is becoming much more apparent to everybody what the remaining tough choices are," he said, adding that he would not be flying to meet the kings of Jordan and Saudi Arabia if he did not believe both sides were grappling with the issues.

"But I cannot tell you when, particularly, the last pieces may decide to fall into place or may fall on the floor and leave the puzzle unfinished," he added.

Kerry appeared boosted by his meeting with Saudi King Abdullah at his winter residence near Riyadh.

"Today, His Majesty was not just encouraging but supported our efforts in (the) hopes that we can be successful in the days ahead," Kerry told reporters after meeting.

During his 10th visit to the region, Kerry had tried to establish what US officials call a "framework" for guidelines for any eventual peace accord.

He has previously asked Israel to reconsider a 2002 Arab peace plan, which it has rejected in the past. The initiative, originally proposed by King Abdullah, offers Israel full recognition in return for giving up land it captured in 1967 and a "just" solution for Palestinian refugees.

Kerry earlier spent an hour with Jordan's King Abdullah in Amman discussing the peace talks, Syria's civil war and violence in Iraq.

The US-brokered Israeli-Palestinian negotiations resumed last July after a three-year halt, with Kerry leading the push for an accord within nine months. But both sides have expressed doubts about his efforts.

Palestinians see a major obstacle in Israel's settlements of West Bank land where they seek statehood. Many Israelis doubt Abbas's credibility as a peace partner, especially as Gaza, the other Palestinian territory, is governed by rival Hamas Islamists who opposes peacemaking.

Foreign Minister Avigdor Liberman, a far-right partner in the coalition government, demanded on Sunday that any peace accord entail an "exchange of populations and territory" with a future Palestinian state.

That referred to Liebrman's long-held vision of Israel keeping blocs of settlements now in the West Bank while redrawing its border so some Arab communities fell under Palestinian jurisdiction.

The Palestinians, and many of their kindred Arabs who make up 20 percent of the Jewish state's population, balk at Israeli bids to revise the boundary of the West Bank which, along with east Jerusalem and the Gaza Strip, was captured in a 1967 war.

Liberman, who had been vocal in his pessimism about chances for a deal, gave qualified backing to Kerry's diplomatic drive.

"Any alternative proposal we'll get from the international community will be much less comfortable for us," he told a meeting of Israeli ambassadors in Jerusalem.

Yasser Abed Rabbo, a senior Palestinian official, called the ongoing talks "serious", but told Voice of Palestine radio: "I can't say now that there's any actual or substantial progress in all the discussions."

Broad Arab support is viewed as crucial if the Palestinians are to make the compromises likely to prove necessary to strike a deal with Israel. Kerry has also said he plans to meet a group of Arab foreign ministers next weekend.

While giving scant detail on his mediation, Kerry has often said progress was being made. But both Israel and the Palestinians have predicted the nine-month target date for a deal will not be met.

Herb Keinon contributed to this report.

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