U.S. President Barack Obama says the United States is prepared to work with Russia and Iran to bring an end to the conflict in Syria but that a resolution to the war must include a “managed transition” away from Syrian President al-Bashar Assad.
In a broad speech stressing the need for international cooperation to ensure global order, Obama told the UN General Assembly's 70th anniversary meeting on September 28 that there is no place for a "tyrant" like Assad, an ally of both Moscow and Tehran, in a post-war Syria.
"The United States is prepared to work with any nation, including Russia and Iran, to resolve the conflict," Obama said. "But we must recognize that there cannot be -- after so much bloodshed and so much carnage -- a return to the pre-war status quo."
His speech came amid a Russian military buildup in Syria that has raised concerns in Washington.
Russian President Vladimir Putin and other officials have said only that Russia was providing weapons and training to Assad's army to help it combat the Islamic State (IS) extremist group, also known as ISIL.
While Obama allowed for cooperation with the Kremlin to bring an end to the Syria crisis, he criticized Assad's backers, saying efforts to defeat IS militants must not bolster a leader "who drops barrel bombs to massacre innocent children."
Obama said, "Assad and his allies can’t simply pacify the broad majority of a population who've been brutalized by chemical weapons and indiscriminate bombings."
"Yes, realism dictates that compromise will be required to end the fighting and stamp out ISIL," he said. "But realism also requires a managed transition away from Assad and to a new leader, and an inclusive government that recognizes that there must be an end to this conflict so that the people of Syria can begin to rebuild."
WATCH: Obama Urges Iran To 'Take A Different Path'
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Obama Urges Iran To 'Take A Different Path'
Addressing the assembly later in the day, Putin said it was a mistake not to cooperate with Assad's forces, which he described the only force "truly fighting" the Islamic State extremist group in Syria.
Obama also criticized Russia's annexation of the Crimea peninsula from Ukraine in March 2014, saying that the land grab could fuel expansionism elsewhere in the world if the international community did not respond decisively to Moscow's actions.
"We recognize the deep and complex history between Russia and Ukraine. But we cannot stand by when the sovereignty and territorial integrity is flagrantly violated. If that happens without consequence in Ukraine, it could happen to any nation gathered here today," he said.
Kyiv and the West also say Russia has sent troops and weapons to fuel the separatist conflict that has killed more than 7,900 people in Ukraine's east since April 2014. Moscow denies the charges.
Ukrainian and rebel forces have blamed each other for repeated breaches of a cease-fire agreement reached in Minsk in February, but both sides are now broadly respecting a renewed truce that came into effect on September 1.
Obama said Washington does not want to isolate Russia. U.S. sanctions targeting Moscow in response to the Ukraine crisis are intended to deter the redrawing of borders and "not part of a desire to return to a Cold War," he said.
He added that Russia's actions have driven Ukrainians into seeking deeper integration with Europe and harmed its own interests.
"Sanctions have led to capital flight, a contracting economy, a falling ruble and the emigration of more educated Russians," Obama said. "Imagine if instead Russia had engaged in true diplomacy and worked with Ukraine and the international community to ensure its interests were protected. That would be better for Ukraine but also better for Russia and better for the world."
WATCH: Obama Defends Sanctions Against Russia
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Obama Defends Sanctions Against Russia
Putin was set to address the Syria issue in a speech to the assembly later in the day, after which he was slated for a face-to-face meeting with Obama.
In an interview broadcast a day earlier in the United States, Putin said "there is no other solution to the Syrian crisis than strengthening the effective government structures and rendering them help in fighting terrorism."
In his speech to the assembly, Putin blamed NATO expansion into Eastern Europe and former Soviet states for creating tensions that led to the mass upheaval in Ukraine that culminated in the ouster of President Viktor Yanukovych in February 2014.
Putin and Obama were set to hold a face-to-face meeting on the sidelines of the General Assembly later on September 28.