US Secretary of State John Kerry said yesterday that any Middle East peace plan would be "fair and balanced", as he sought to counter Israeli and Palestinian claims the US was biased towards the other side. And on a day of whirlwind diplomacy, flying thousands of kilometres between key Arab allies, the top US diplomat likened his intense efforts to broker a deal to a puzzle. "In the end, all of these core issues fit together like a mosaic, like a puzzle and you can't separate out one piece or another," Kerry said in Jerusalem before flying to Amman early yesterday, and later to Saudi Arabia, seeking backing for his proposals. Each piece was interlinked, he stressed, and depended on the compromises the other side might be prepared to make. "And there's always tension as to when you put your card on the table as to which piece you're willing to do, when and how," said Kerry. But he warned his efforts could ultimately fail, saying he could not tell when "the last pieces may decide to fall into place, or may fall on the floor, and leave the puzzle unfinished. That's exactly what makes this such a challenge." Kerry has already spent three intense days shuttling between Israel's Prime Minister Benjamin Netanyahu and Palestinian president Mahmoud Abbas. And yesterday he met first with Jordan's King Abdullah II to update him on the talks so far. Jordan borders the occupied West Bank and under its 1994 peace treaty with Israel the Hashemite kingdom is recognised as playing a historic role in the guardianship of Muslim sites in east Jerusalem. Kerry is on his 10th visit to the region since taking office less than a year ago, and kick-started nine months of direct negotiations in July after a three-year hiatus. But bitter recriminations between the two sides, who have refused to budge on their mostly irreconcilable demands, have burst into the open during this trip. Israeli and Palestinian officials have both said the emerging proposals appear to favour the other side. "I can guarantee all parties that President (Barack) Obama and I are committed to putting forward ideas that are fair, that are balanced, and that improve the security of all the people of this region," Kerry insisted. Refusing to outline any specific details, Kerry urged Israeli and Palestinian leaders to make "tough choices" to bring about a lasting peace after decades of conflict. "We are now at a point where the choices narrow down, and the choices are obviously real and difficult."