A series of last-ditch diplomatic initiatives have failed to deflect a Palestinian effort to seek recognition of statehood at the United Nations, dashing White House officials’ hopes of avoiding a politically painful U.S. veto at the U.N. Security Council.

Two of the Obama administration’s top Middle East advisers traveled home from the region on Thursday after two days of largely fruitless meetings aimed at averting a U.N. showdown two weeks from now, administration officials acknowledged. The visits followed an appeal by Secretary of State Hillary Rodham Clinton, who telephoned Palestinian Authority President Mahmoud Abbas on Tuesday to urge him to change course.

Palestinian officials rejected the U.S. overtures on Thursday, saying that neither diplomacy nor threats — including a vow by key congressional leaders to cut off U.S. aid — would deter a plan to seek U.N. membership for a Palestinian state at an upcoming Security Council session.

“We told them that we don’t want a confrontation, neither with the Americans nor with anybody else,” said Abbas, speaking to reporters in Ramallah. “They are our friends. We don’t want a confrontation, but let us express our ideas, our hope. We are a people without hope now.”

The Obama administration has warned that it would veto the move, putting the White House at odds with its stated support of political rights for Arabs and an independent homeland for Palestinians.

Palestinian Authority President Mahmoud Abbas, pictured above in Berlin earlier this year.) (Carsten Koall/Getty Images)

With diplomatic efforts in tatters, U.S. officials and Middle East experts said they were at a loss for how a U.S. veto could be avoided.

“It’s difficult to be overly optimistic, to put it mildly,” former senator George J. Mitchell (D-Maine), who until this year was the Obama administration’s special envoy on Middle East peace, said in a grim assessment Thursday before a Georgetown University panel on resolving the impasse.

With the peace process stalled since last September, Palestinian officials decided earlier this year to move their quest for statehood to the world body. Abbas is expected to make a formal request for U.N. membership at the Security Council as early as Sept. 21.

If the initiative is blocked, as expected, by a U.S. veto, Palestinian officials say they could appeal to the General Assembly, where no single nation can block action and where sympathy for the Palestinian cause is widespread.

The General Assembly cannot approve membership without Security Council approval, but it probably would support a weaker measure upgrading the Palestinian Authority’s status from “observer” to “non-member state,” on par with the Vatican. That would clear the way for the Palestinians to join U.N. bodies and conventions, and it could enable them to pursue claims against Israel in the International Criminal Court.

Although the White House officially supports statehood, it opposes what administration officials argue would be a merely symbolic gesture that could set back peace efforts and do little to help Palestinians. State Department spokeswoman Victoria Nuland on Thursday repeated the U.S. veto threat, saying the U.N. bid would “make it harder to get back to talks.”

“We are seeking a result in the region that is consensual between the two parties, that is lasting, that is durable, that leads to security,” she told reporters.

A senior administration official involved in Middle East policy discussions acknowledged that a U.N. clash appeared all but inevitable after unsuccessful talks between Abbas and two senior U.S. diplomats: special Middle East envoy David Hale and White House adviser Dennis Ross. The two met with Israeli and Palestinian officials during a two-day visit that ended late Wednesday.

The official, who spoke on the condition of anonymity to discuss sensitive diplomacy, said the White House had reached out to about 100 governments around the world in an effort to persuade them to oppose the Palestinian bid.

“We don’t think this is good for anyone — not for Israel, certainly not for the Palestinian people,” the official said. He noted that, even as the U.S. diplomatic initiative floundered, efforts continued under the auspices of the “quartet” — the United States, the United Nations, the European Union and Russia — to work out a deal to resume direct negotiations. “We’re not finished yet,” the official said.

Abbas said the Palestinians remain committed to peace negotiations, but he vowed that the U.N. effort will proceed even if a formula for resuming talks is found.

“I don’t think that it’s workable,” he said of efforts by international mediators to come up with a last-minute diplomatic package to head off the U.N. bid. “They came too late.”

He added, “We will go to the U.N., and we will return back to talk” with the Israelis.

Abbas sought to allay concerns that a U.N. vote in favor of Palestinian statehood would lead to unrest in the West Bank and possible confrontations with Israeli troops and settlers.

“From our side, no confrontations, no chaos,” he said.