President Obama on Thursday pushed Arab nations to provide more political and financial support for the Middle East peace effort, warning that they should not risk the failure of the latest initiative if they truly seek an independent Palestinian state and stability across the region.

Obama deplored efforts — assisted by some Arab and Muslim countries — to isolate or "delegitimize" Israel.

"Those who long to see an independent Palestine rise must stop trying to tear Israel down," Obama said in a morning address to the United Nations General Assembly. "It should be clear to all that efforts to chip away at Israel's legitimacy will only be met by the unshakeable opposition of the United States."

But Obama also asked for a sacrifice by the Israelis, using the U.N. forum to renew his call for the continuation of Israel's freeze — set to expire Sept. 26 — on construction in disputed areas.

"Our position on this issue is well known," Obama said. "We believe that the moratorium should be extended. We also believe that talks should press on until completed."

Those who support self-government of the Palestinians should help the Palestinian Authority by giving political and financial support to build the institutions of their state, Obama said. Compromise will be hard, he said, but it is better than the alternative.

"If an agreement is not reached, Palestinians will never know the pride and dignity that comes with their own state," Obama said. "Israelis will never know the certainty and security that comes with sovereign and stable neighbors who are committed to coexistence."

Palestinian Authority President Mahmoud Abbas was present in the chamber for Obama's speech, but Israeli Prime Minister Benjamin Netanyahu did not come to New York for the assembly.

The remarks came in a speech in which Obama spoke broadly of the international community's shared responsibility to support democracy and human rights, and he called upon world leaders not to "stand idly by" as dissidents are imprisoned and protesters are beaten.

He praised his administration's attempts to fight threats from extremist groups without deploying large American armies, obliquely referencing a sweeping strategy that includes collaboration with foreign governments and strikes by unmanned aircraft against terrorist targets. The administration does not publicly discuss the drone program.

Obama's appeal to Arab leaders comes at a time when it appears the 3-week-old U.S.-led Mideast peace initiative could collapse over the issue of the moratorium. Leaders of the Palestinian Authority have threatened to abandon the negotiations if the moratorium is allowed to expire.

As that issue simmers, the Obama administration has been trying to build support in the Arab world for the peace talks. Without it, the weak Palestinian Authority leadership may not have the stature to make risky and unpopular compromises with the Israelis.

Obama is pressing for cooperation on a range of security and economic matters during his three days at the United Nations. He also met privately with Chinese and Japanese leaders Thursday, discussing the issue of Chinese currency as well as maritime sovereignty disputes in the South China Sea.

A constant in all of Obama's one-on-one meetings with world leaders this week is the push to curtail the Iranian nuclear program, and in his speech the president again called on Tehran to confirm the "peaceful intent" of its nuclear ambitions.

But no single issue seemed more important to Obama this week than peace in the Mideast, an initiative in which he has invested plenty of his personal and political capital.

In his second address to the full assembly since taking office, Obama devoted nearly a third of his time to the peace process, urging not just the principals to compromise but also their neighbors throughout the region and beyond.

Some countries, including the United Arab Emirates, Qatar and Saudi Arabia, are behind on their promised financial aid to the Palestinian Authority, to the dismay of the U.S. The Arab countries suspect that the Palestinian government will waste the money, and some of them also have ties to Hamas, the militant Palestinian group that controls the Gaza Strip and is a rival to Fatah, the party that controls the West Bank.

Obama urged nations that have signed on to the Arab peace initiative to "make it real" by normalizing relations with Israel.

"That kind of political support is important," U.S. deputy national security advisor Ben Rhodes said. "It helps give President Abbas the support he needs to go forward."

By dwelling so much on the Arab-Israeli conflict, Obama probably raised expectations about the prospects for peace, said Aaron David Miller, a former Mideast peace negotiator and a scholar at the Woodrow Wilson International Center for Scholars.

"With language like, 'I refuse to accept that alternative,' Obama has also placed pressure not just on Abbas and Netanyahu, but on himself," Miller said. "That's sometimes unwise."

By so strongly emphasizing his commitment and his stake in the process, Obama has put himself in the middle of the matter, Miller said.

"That's OK if Abbas and Netanyahu are prepared to get in there with him and make the right decisions," he said. "If not, he'll look naive and, worse, like he's failed."

Hours after Obama's appearance, the U.S. delegation walked out of a speech by Iranian President Mahmoud Ahmadinejad after he suggested that the U.S. government may have carried out the Sept. 11, 2001, attacks to ensure Israel's survival.

Ahmadinejad said there were three theories about how the attacks happened.

One was that a "powerful and complex terrorist group" had executed them. Another was that "some segments within the U.S. government orchestrated the attack to reverse the declining American economy and its grips on the Middle East … in order also to save the Zionist regime."

A third, he said, was that a terrorist group had carried out the attacks, but that the U.S. government supported it and took advantage of the development.

Two U.S. officials listening to the speech rose after the second theory and walked out of the room, trailed by diplomats from some allied countries.

The U.S. delegation issued a statement saying, "Rather than representing the aspirations and goodwill of the Iranian people, Mr. Ahmadinejad has yet again chosen to spout vile conspiracy theories and anti-Semitic slurs that are as abhorrent and delusional as they are predictable."