WASHINGTON — Jason Greenblatt, a key architect of President Donald Trump's troubled Israeli-Palestinian peace plan, announced his resignation Thursday.

His departure places another question mark over the much-delayed initiative, which the White House has touted as the "opportunity of the century," but has yet to see the light of day and has been rejected in advance by the Palestinians.

Greenblatt, who worked for two and a half years alongside Trump's powerful son in law Jared Kushner, said in a statement that his plan had been "a vision for peace." Kushner lauded him as someone "trusted and respected by all of the leaders throughout the region."

A senior administration official said Greenblatt was going to spend more time with his family but left on good terms and "holds the confidence of the president."

For all the warm words, Greenblatt's departure only adds to the sense that Trump's promise to transform the US approach to the Israeli-Palestinian conflict is floundering.

Just a week ago, Greenblatt signaled the latest pushback to the plan's unveiling, saying it would not be released until after Israel's Sept. 17 election, which will decide whether Trump ally Prime Minister Benjamin Netanyahu stays in power.

Ilan Goldenberg, a Middle East negotiator in former US president Barack Obama's government, said another election — the US presidential polls in November next year — could be the real reason for a hold up.

"Let me translate this for you," he tweeted after Greenblatt's announcement. "Kushner's Mideast peace plan will not see the light of day before November 2020 if at all (my bet is on never)."

Trump has repeatedly boasted that he is the most pro-Israeli US president in history. He has slashed aid to the Palestinians, while making big concessions to the Israelis, including formalizing US recognition of the divided city of Jerusalem as the Israeli capital.

According to the Republican, his concept for ending the Israeli-Palestinian conflict revolves around encouraging massive economic investment, hoping that money will speak louder than political divides.

However, Palestinian leaders have dismissed the plan as one-sided and failing to address their wish to end Israeli occupation and the expansion, encouraged by Netanyahu, of Jewish settlements on Palestinian land.

Greenblatt "was an apologist for the most extreme, hard-line government in the history of Israel," Hanan Ashrawi, a senior Palestinian official, told AFP.

"Nobody ever saw him as evenhanded or neutral in any way. He was totally committed not to peace but to the justification of all Israeli violations," she said. "I think the Palestinians as a whole are going to say good riddance."

Israeli authorities, however, were sorry to see him go. Netanyahu thanked Greenblatt "for his dedicated work for security and peace and for never hesitating to tell the truth about the state of Israel to its detractors."

A senior Trump administration official echoed that sentiment, underlining Greenblatt's role in the steadily intensifying nature of Washington's support for Israel.

"Jason was instrumental, together with others in the administration, when the president recognized Jerusalem as the capital of Israel, moved the US embassy to Jerusalem, and recognized Israeli sovereignty over the Golan Heights," the official said.

"Jason has also been instrumental in helping to reframe the discussions about the conflict, using the approach that a real peace can only be built on truth."

The question is when Greenblatt's plan will finally emerge and whether it will gain traction. According to the White House official, "the vision is now complete and will be released when appropriate." — AFP