Diplomats struggled Thursday evening to devise a way to restart Middle East peace talks, apparently without success, as Palestinian leaders prepared the formal launch of their emotionally charged campaign for membership to the United Nations.

With the U.N. bid just hours away, U.S., European and Middle Eastern officials huddled in hotel rooms to try resolve differences about how to limit the discord over the membership quest — and perhaps even leverage the crisis to force Israel and the Palestinians back to the bargaining table after nearly a year apart.

The diplomatic wrangling occurred against a backdrop of pageantry and speechmaking at the U.N. General Assembly, including an incendiary address by Iranian President Mahmoud Ahmadinejad. The Iranian leader triggered a mass exodus from the U.N. chamber after he suggested that larger conspiracies were behind the Nazi Holocaust and the Sept. 11, 2001, attacks.

The search for a breakthrough on Middle East peace talks came on the eve of a scheduled speech by Palestinian Authority President Mahmoud Abbas, in which he is expected to petition the U.N. Security Council to grant membership to a Palestinian state. The move is opposed by Israel and by the Obama administration, which has argued that a statehood bid could hinder the resumption of direct negotiations to resolve the conflict.

Obama administration officials, acknowledging fading hopes for stopping Abbas from proceeding with the membership bid, said the chief concern now is to prevent the Palestinian initiative from driving the two sides further part — and perhaps crushing any hopes for a peace deal in the foreseeable future.

“Regardless of what happens tomorrow in the United Nations, we remain focused on the day after,” Secretary of State Hillary Rodham Clinton told reporters during a news conference with Tunisian Foreign Minister Mouldi Kefi.

Clinton, who met separately with Abbas and Israeli Prime Minister Benjamin Netanyahu late Wednesday, said both leaders expressed a commitment to resuming direct negotiations to resolve the conflict’s most vexing issues, including final borders, the right claimed by Palestinian refugees and their descendants to return to what is now Israel, and the status of Jerusalem.

Yet it remained unclear whether the two sides could overcome the deep distrust that has stalled negotiations for more than a year and reach agreement on a Palestinian request that Israel cease building settlements in the occupied West Bank. Netanyahu imposed a temporary moratorium on settlements last year at some political risk, but when it was not extended, negotiations collapsed.

“They both recognize that there has to be a resolution of the outstanding issues to produce a functioning Palestinian state,” Clinton said. She added: “We will leave no effort or stone unturned in our commitment to achieving that.”

Talks among members of the Quartet of Mideast peace mediators — the United States, the European Union, Russia and the United Nations — ended late Thursday, but there was sufficient progress that a new round of discussions was scheduled for early Friday, just ahead of Abbas’s speech, a senior administration official told reporters.

In his Wednesday address to the General Assembly, President Obama emphasized his “unshakable” support for Israel and rejected the Palestinians’ bid to have the United Nations recognize the West Bank, the Gaza Strip and East Jerusalem as their state.

The speech drew strong support from Netanyahu, who called Obama’s opposition to the Palestinian diplomatic effort a “badge of honor.” But some traditional allies, including France, proposed elevating the Palestinians’ status in the United Nations as a way of trying to break decades of stalemate, a move Obama and Israel oppose.

In his remarks Thursday to the General Assembly, Ahmadinejad swiped at Israel and its supporters, who he said imposed “60 years of war, homelessness, terror and mass murder on the Palestinian people.” It was one of many incendiary lines in a 30-minute speech that blamed the West for slavery, two world wars and the global economic crisis. And he also told the Associated Press that the planes by themselves couldn’t have brought down the World Trade Center towers on Sept. 11, 2001.

The Iranian leader, known for his bomb-throwing rhetoric, criticized the Obama administration for killing Osama bin Laden, suggesting that the al-Qaeda leader could have been the star witness at a trial that would reveal the true culprits behind the attacks.

“Instead of assigning a fact-finding team, they killed the main perpetrator and threw his body into the sea,” Ahmadinejad said. Meanwhile, those who raised questions about Sept. 11 or the Holocaust, he said, were “threatened with sanctions and military action.”

His words sent diplomats streaming for the exits, starting with the U.S. delegation and followed by dozens of Europeans and others. More than a third of the General Assembly seats were empty by the time Ahmadinejad finished speaking, to polite applause.

The Iranian president had recently made conciliatory gestures to the West, including his support for a decision to free Americans Shane Bauer and Josh Fattal, who were arrested in 2009 after apparently straying into Iranian territory during a hike along Iraq’s border. But no olive branches were in evidence during his sharply worded speech, which was accompanied by finger-wagging and dramatic hand gestures.

“Do these arrogant powers really have the competence and ability to run or govern the world?” he asked, referring to the United States and the former colonial powers of Europe. In an apparent reference to the Western-led military intervention in Libya, he added: “Can the flower of democracy blossom from NATO’s missiles, bombs and guns?”

Staff writer Scott Wilson contributed to this report.