They may have clinked wine glasses, but the pleasantries were spare between U.S. President Barack Obama and Russian President Vladimir Putin.
In their speeches before the UN General Assembly on September 28, the two leaders traded criticism over the ongoing conflicts in Syria and Ukraine, accusing one another’s governments of fueling global instability before tapping their glasses at a luncheon for world leaders.
In a thinly veiled barb aimed at Moscow, Obama chided countries for backing Syrian President Bashar al-Assad, a longtime Russian ally that the Kremlin has bolstered in recent weeks by moving advanced weaponry, aircraft, and military personnel into war-torn Syria.
The U.S. president said "some major powers assert themselves in ways that contravene international law" and erode "democratic principles and human rights," adding that "we're told that such retrenchment is required, to beat back disorder."
"In accordance with this logic, we should support tyrants like Bashar al-Assad, who drops barrel bombs to massacre innocent children," Obama said.
WATCH: Obama Calls For Transition 'Away from Assad' in Syria
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Obama Calls For Transition 'Away from Assad' in Syria
He added that Washington is willing to work with Russia and another Assad ally, Iran, to bring an end to the conflict in Syria but that any resolution to the war must include a "managed transition" away from Assad.
Speaking after Obama, meanwhile, Putin called it "an enormous mistake to refuse to cooperate" with Assad's government to combat Islamic State (IS) militants.
"We should finally acknowledge that no one but President Assad's armed forces and the Kurdish resistance are truly fighting the Islamic State and other terrorist organizations in Syria," Putin said.
WATCH: Putin Calls It A Mistake Not To Work With Assad
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Putin Calls It A Mistake Not To Work With Assad
Russian surveillance drones have been spotted over several battlefield areas in Syria, and some of the aircraft are interceptor jets, which has raised eyebrows since Islamic State does not have an air force.
The size and scope of the Russian deployment -- its largest outside the former Soviet Union in decades -- has stoked suspicions by Washington and others that Moscow is seeking a longer-term presence in Syria, possibly aimed at thwarting U.S. initiatives in the region.
Those suspicions deepened over the weekend, with the announcement by Iraq that it would share "security and intelligence" with Russia and Iran in the fight against Islamic State, an announcement that caught the United States off guard.
Putin dismissed those concerns, saying "it's not about Russia's ambitions," but rather "about the recognition of the fact that we can no longer tolerate the current state of affairs in the world."
Neither Putin nor Obama were in the UN assembly hall for each other's speeches, in which they outlined sharply different worldviews about how to resolve crises around the globe.
While Obama stressed that repressive governments are inherently unstable and eventually crumble into chaos, Putin made repeated allusions to the United States, which he identified by name only once, and the West more broadly as the source of destructive meddling in other countries' affairs.
He accused Washington of providing arms to Assad's opponents who then defect to fight alongside IS extremists.
He also suggested that the United States is to blame for the instability in Libya, where U.S.-backed air power helped pave the way for the ouster of Muammar Qaddafi, and in Iraq, following the 2003 invasion.
He said pointedly that Islamic State fighters include former Iraqi military officers and Libyan soldiers, as well as moderate Syrians.
Ukraine Standoff
Obama and Putin also clashed over Russia's annexation of the Crimea peninsula from Ukraine in March 2014.
Obama said 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 are "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, meanwhile, echoed the Kremlin's longstanding accusations that the United States is exporting revolutions in countries of the former Soviet Union.
He blamed NATO and its 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.
"They offered the poor Soviet countries a false choice: either to be with the West or the East," Putin said. "Sooner or later this logic of confrontation was bound to spark a grave geopolitical crisis. This is exactly what happened in Ukraine, where the discontent of the population with the current authorities was used and a military coup was orchestrated from outside that triggered a civil war as a result."
Putin and Obama, who were set to meet face-to-face in a bilateral meeting later in the day, sat close to one another at the luncheon following the morning's speeches, with UN Secretary General Ban Ki-Moon seated between them.
It was after a toast by the secretary-general that the two leaders clinked glasses. A photograph of the moment shows Putin smiling, while Obama is not.