(reuters) -- Trump reversed decades of U.S. policy on Wednesday with his announcement and instructions to begin the process of moving the embassy in Tel Aviv to al-Quds, despite warnings that it would drive the wedge between Israel and the Palestinians deeper.

The Saudi royal court described the decision as “unjustified and irresponsible” and “a big step back in efforts to advance the peace process.”

But Arab officials privately say that Riyadh appears to be on board with a broader U.S. strategy for an Israeli-Palestinian peace plan still in its early phases of development.

Four Palestinian officials, who spoke on condition they not be named, said Saudi Crown Prince Mohammed bin Salman and Palestinian President Mahmoud Abbas discussed in detail a grand bargain that Trump and Jared Kushner, the president’s son-in-law and adviser, are expected to unveil in the first half of 2018.

One official said Prince Mohammed asked Abbas to show support for the U.S. administration’s peace efforts when the two met in Riyadh in November.

Another Palestinian official said Prince Mohammed told Abbas: “Be patient, you will hear good news. This peace process will go ahead.”

The U.S.-Saudi relationship has improved dramatically under Trump, partly because the leaders share a vision of confronting Riyadh’s arch-rival Iran more aggressively in the region.

Kushner, 36, whose father knew Israeli leader Benjamin Netanyahu, has also nurtured strong personal ties with the 32-year-old crown prince as he asserts Saudi influence internationally and amasses power for himself at home.

The Saudi royal court did not respond to requests for comment. A White House official said Kushner did not ask the crown prince to talk to Abbas about the plan.

The Palestinian officials said they were concerned that the proposal that Prince Mohammed communicated to Abbas, which purportedly came from Kushner, presents exactly that scenario.

As told to Abbas, the proposal included establishing “a Palestinian entity” in Gaza as well as the West Bank administrative areas A and B and 10 percent of area C, which contains Jewish settlements, a third Palestinian official said.

Jewish settlements in the West Bank would stay, there would be no right of return, and Israel would remain responsible for the borders, he said.

The proposal appears to differ little from existing arrangements in the West Bank, widening Palestinian control but falling far short of their minimum national demands.

“This is rejected by Palestinians. Abu Mazen (Abbas) explained the position and its danger to the Palestinian cause and Saudi Arabia understood that,” the official said.

The White House official denied that Kushner communicated those details to Prince Mohammed: “It does not accurately reflect any part of the conversation.”

(Photo: This file photo shows Palestinian President Mahmoud Abbas (L) meeting with Saudi Crown Prince Mohammad bin Salman.)