Tony Blair has stepped down as the Quartet's Middle East peace envoy, officials said, leaving a post that began with great promise but which struggled to deliver dramatic changes in its quest to promote peace between Israel and the Palestinians.
The departure reflected the dire state of Middle East peace efforts, which have been stalled for years and show no signs of resuming following the formation of Israeli prime minister Benjamin Netanyahu's new government. A top Palestinian official said he was "happy" Mr Blair was leaving, accusing him of ineffectiveness and caving in to Israeli pressure.
Officials familiar with the work of the Quartet in the region said former British prime minister Mr Blair had written a letter to United Nations chief Ban Ki-moon to confirm his resignation.
A formal announcement is expected later today at a meeting of Quartet officials in Brussels. At midday today, UN spokesman Stephane Dujarric said he could not yet confirm receipt of the resignation letter.
The Quartet - which includes the US, the European Union, Russia and the United Nations - appointed Mr Blair to the post in 2007 with the goal of helping develop the Palestinian economy and institutions.
The mission was meant to prepare the groundwork for the establishment of a Palestinian state alongside Israel as part of a peace agreement.
But Mr Blair quickly found himself fighting small battles with Israel over the movement of Palestinian goods and people in the West Bank, and dealing with the difficulties of a Gaza Strip ruled by the Hamas militant group and blockaded by Israel and Egypt. Hamas, which is shunned as a terrorist group by the US and EU, seized control of Gaza from the rival government of Palestinian president Mahmoud Abbas shortly before Blair took office.
When Mr Blair first took office, then-Israeli prime minister Ehud Olmert and Abbas were conducting a round of peace talks that both sides have said made significant progress.
But those talks ultimately failed, and since Mr Netanyahu's election in 2009, repeated attempts at reviving talks have flopped.
Mr Netanyahu's new government is dominated by parliamentary hard-liners who oppose Palestinian independence, leaving the goal of a two-state solution as elusive as ever.
One official said Mr Blair had suffered "frustration" with the limited authority of his mandate, which did not include a political role. The official also said that Mr Blair felt his office has a strong leadership team and that now is the right time to move on.
According to his office's website, Mr Blair's office succeeded in helping remove dozens of Israeli checkpoints in the West Bank, easing the movement of workers and Palestinian products to markets.
He also helped boost tourism in the West Bank town of Bethlehem, helped secure thousands of permits for Palestinian labourers to work in Israel, helped engineer a 350 million US dollar (£228 million) mobile phone investment in the West Bank, creating thousands of jobs and also pressed Israel to allow limited exports out of blockaded Gaza.
Even so, his efforts often disappointed the Palestinians, who accused him of being ineffective and caving in to Israeli demands too easily.
"I'm happy that Tony Blair is leaving. For the entire eight years, Tony Blair didn't make any contribution to Palestine," said Nabil Shaath, a senior Palestinian official. "He never proposed anything that the Israelis didn't agree to, and the entire time he only represented himself. And he worked only to satisfy the Israelis and the Americans."
Mr Netanyahu's office declined to comment.
The official said that Mr Blair's resignation would go into effect in June, but that he hopes to play an "informal" role in promoting the Quartet's vision of a two-state solution. One area where he could help is developing relations between Israel and the wider Arab world, the official said.