"If the U.S.is so concerned about Palestinian well-being, then why did they carry out these punitive measures against us?", senior Palestine Liberation Organisation official Hanan Ashrawi said in Ramallah.
However, there have been top-level meetings in the past at which political solutions have been discussed.
But Oman was the first Gulf state to receive Israeli Prime Minister Benjamin Netanyahu in October 2018.
The $50bn (£39bn) pledged, effectively as a start-up fund for the region's Palestinians, was less than enthusiastically received in Jordan, Egypt and in Lebanon - where leaders in Beirut, not usually inclined to turn away from a $6bn money pot, dismissed the pitch as a shameless bribe.
As for the criticism directed at Trump's decision to recognise occupied Jerusalem as the capital of Israel, Kushner asserted that "the United States and Congress have had the right to enact this legislation for years".
'Peace, political stability and re-establishment of trust between all the parties involved are essential pre-requisites to the success of any economic plan for the region'.
"Stability and security is key to investment in every country where we go", said Selim Bora, president of the Turkish investment firm Summa.
"Instead of repurposing old ideas and claiming them as their own, we strongly urge the Trump administration to reaffirm its support for a two-state solution, which has been USA policy for decades".
In an opinion piece published at the American political magazine Politico, Ami Ayalon, a former director of the Israeli security agency Shin Bet, Gilead Sher, former chief of staff for Israeli Prime Minister Ehud Barak and senior peace negotiator, and Orni Petruschka, a high-tech entrepreneur and think tank cofounder in Israel called Trump's plan a "dangerously simplistic approach to a complicated situation".
Palestinian business groups and the Palestinian Authority have boycotted the plan.
Saudi Arabia, the United Arab Emirates, Bahrain, Jordan, Egypt and Morocco were among the Arab countries attending Kushner's summit - but of those countries, only Saudi Arabia, the UAE and Bahrain dispatched high-level officials to represent them.
Israeli experts said the plan sounds great on paper but that under the surface it was "all form and no substance". Trump's team has consistently refused to commit to it. Protesters burnt pictures of Trump, Kushner and Netanyahu and others criticised Arab states for attending.
However, bin Alawi has made a number of statements in favour of improved Arab relations with Israel in recent months.
"They are traitors. We decide our fate and no one else".
"The workshop is being held in Bahrain, home of the US Navy's Fifth Fleet, at a time of heightened tension between Tehran and Washington and its Gulf allies".
The Palestinians cut ties with the White House after Trump recognized contested Jerusalem as Israel's capital in December 2017 and say they will not accept a peace proposal from an administration they see as biased toward Israel.
Neither the Israeli nor Palestinian governments attended the meeting, which took place amid a years-long stalemate in other global efforts to resolve a conflict that has lasted more than seven decades.
The second day of the conference will hear from business leaders and the heads of global development banks on the prospects for the Palestinian plan.
Oil-rich Gulf states, which would be expected to foot the bill if the plan moves ahead, sent high-powered delegations but other nations were more discreet. Breaking with the global consensus, Trump in 2017 recognized Jerusalem as Israel's capital, infuriating the Palestinians and other Arabs.
"Jared is not a politician, he's a real estate man", the businessman said on condition of anonymity.
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