The officials, who are familiar with the work of the Quartet in the region, said Blair had written a letter to UN chief Ban Ki-moon to confirm his resignation. The officials spoke on condition of anonymity pending a formal announcement, which was expected later today at a meeting of Quartet officials in Brussels.
The Quartet which includes the US, the European Union, Russia and the United Nations appointed 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.
One official said Blair had suffered "frustration" with the limited authority of his mandate. The official also said that 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, 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.
The official said that Blair remains committed to the Quartet's vision of a two-state solution and hopes to play an "informal" role in promoting peace. One area where he could help is developing relations between Israel and the wider Arab world, the official said.