GWEN IFILL: Diplomatic dilemmas in Syria and Iran occupied center stage today at the United Nations, as President Obama and other world leaders met for their annual meeting.
Chief foreign affairs correspondent Margaret Warner is there.
PRESIDENT PRESIDENT OBAMA: It's an insult to human reason and to the legitimacy of this institution to suggest that anyone other than the regime carried out this attack.
MARGARET WARNER: President Obama came to the U.N. gathering asserting he'd been entirely right to threaten military retaliation last month over Syria's alleged use of chemical weapons against civilians.
PRESIDENT OBAMA: Now, I know that in the immediate aftermath of the attack, there were those who questioned the legitimacy of even a limited strike in the absence of a clear mandate from the Security Council.
But without a credible military threat, the Security Council had demonstrated no inclination to act at all.
MARGARET WARNER: And now, said the president, it's essential that the Council does act to make sure the Assad regime hands over its chemical stockpile for disposal, as outlined in a U.S./Russian agreement.
PRESIDENT OBAMA: There must be a strong Security Council resolution to verify that the Assad regime is keeping its commitments. And there must be consequences if they fail to do so.
If we cannot agree even on this, then it will show that the United Nations is incapable of enforcing the most basic of international laws.
MARGARET WARNER: But, in Moscow today, it was clear the U.S. and Russia remain at odds over whether any U.N. resolution should threaten military force or other punitive steps against Syria if it fails to comply.
Russian Deputy Foreign Minister Sergei Ryabkov:
SERGEI RYABKOV, Russian Deputy Foreign Minister (through interpreter): In this situation, the attempts of the Americans actively supported by the English and French to push the U.N. Security Council to craft a resolution that would obtain a direct danger to Syria is absolutely illogical.
MARGARET WARNER: Russia has joined the U.S. in pursuing a negotiated settlement to the two-and-a-half year conflict, but also has stood by its longtime ally President Bashar Assad against calls for him to step down.
Back at the U.N. today, President Obama was dismissive.
PRESIDENT OBAMA: The notion that Syria can somehow return to a pre-war status quo is a fantasy. So, it's time for Russia and Iran to realize that insisting on Assad's rule will lead to directly to the outcome that they fear, an increasingly violent space for extremists to operate.
MARGARET WARNER: Turkey also wants regime change in Syria, and Turkish President Abdullah Gul urged the U.N. to focus on stopping not just the use of chemical weapons, but the war itself.
PRESIDENT ABDULLAH GUL, Turkey: Now we speak of over 100,000 deaths. If we cannot stop this conflict now, let's assure that we will be talking about twice that number next year. I cannot emphasize this enough. Agreement on chemical weapons must not be allowed to substitute -- substitute for a comprehensive foolproof strategy to address the situation in Syria.
MARGARET WARNER: U.N. Secretary-General Ban Ki-Moon also appealed for an end to the killing, and, to that end, he urged a halt to all shipments of weapons into Syria.
BAN KI-MOON, United Nations Secretary-General: We can hardly be satisfied with destroying chemical weapons while the wider war is still destroying whole Syria. I appeal to all states to stop fueling the bloodshed and to end the arms flows to all the parties.
MARGARET WARNER: The president's other major focus, the prospect of a new diplomatic initiative to resolve the standoff over Iran's nuclear program. The country's newly elected president, Hassan Rouhani, has shown signs of moderation and has spoken of being willing to negotiate over the nuclear issue.
Mr. Obama said he welcomed the change in tone.
PRESIDENT OBAMA: We are encouraged that President Rouhani received from the Iranian people a mandate to pursue a more moderate course. And given President Rouhani's stated commitment to reach an agreement, I am directing John Kerry to pursue this effort with the Iranian government in close cooperation with the European Union, the United Kingdom, France, Germany, Russia, and China.
The roadblocks may prove to be too great, but I firmly believe the diplomatic path must be tested.
MARGARET WARNER: But, at the same time, the president insisted Iran's words must be backed up by actions that are transparent and verifiable.
PRESIDENT OBAMA: We are not seeking regime change and we respect the right of the Iranian people to access peaceful nuclear energy. Instead, we insist that the Iranian government meet its responsibilities under the Nuclear Non-Proliferation Treaty and U.N. Security Council resolutions.
MARGARET WARNER: President Rouhani plans to meet with European leaders on the sidelines of the U.N. session. But he won't be meeting with President Obama. A senior administration official said today that the Iranians told the U.S. it was -- quote -- "too complicated" to meet this week.
A short time ago, Iranian President Rouhani spoke at the United Nations, striking a conciliatory tone on his country's nuclear program. He also said that he hopes President Obama wouldn't be swayed by -- quote -- "war-mongering pressure groups."
PRESIDENT HASSAN ROUHANI, Iran (through interpreter): Nuclear weapons and other weapons of mass destruction have no place in Iran's security and defense doctrine and contradict our fundamental religious and ethical convictions.
Our national interests make it imperative that we remove any and all reasonable concerns about Iran's peaceful nuclear program. We can arrive at a framework to manage our differences.