ENNISKILLEN, Northern Ireland — Deep differences over Syria’s fierce civil war clouded a summit of world leaders Monday, with President Vladimir Putin of Russia defiantly rejecting calls from the United States, Britain, and France to halt his political and military support for Syrian leader Bashar Assad’s regime.
But there were also fissures among the three Western nations, despite their shared belief that Assad must leave power. Britain and France appear unwilling — at least for now — to join President Obama in arming the Syrian rebels, a step the US president reluctantly finalized last week.
The debate over the Syria conflict loomed large as the two-day summit of the Group of Eight industrial nations opened at a lakeside resort in Northern Ireland.
The lack of consensus even among allies underscored the vexing nature of the two-year conflict in Syria, where at least 93,000 people have been killed as rebels struggle to overtake Assad forces buttressed by support from Hezbollah, Iran, and Russia.
Obama and Putin, who already have a frosty relationship, did little to hide their differing views on the matter while speaking to reporters after one-on-one talks on the sidelines of the summit Monday evening. The two-hour meeting marked the first time the leaders had met in person since last year.
‘‘We do have different perspectives on the problem,’’ Obama said of their divergent views on Syria. The Russian leader, speaking through a translator, agreed, saying, ‘‘our opinions do not coincide.’’
While Putin did not publicly criticize the US decision to arm the opposition during his meeting with Obama, he exhibited far less restraint Sunday after his meeting with Prime Minister David Cameron of Britain, characterizing the rebel fighters as extremists.
Perhaps signaling another fight to come between the United States and Russia, the foreign ministry in Moscow said Russia would veto a motion to set up a no-fly zone if the United States sought authorization from the United Nations Security Council.
The no-fly zone would seek to stop Assad from using his air power to crush rebel forces or kill civilians. But European nations are so far opposed to that idea, and Obama’s own aides have publicly questioned the feasibility, given Assad’s air defenses and the significant costs of such a program.
In Syria on Monday, a car bomb targeting a checkpoint near a military airport in an upscale neighborhood of Damascus killed 10 soldiers, and Assad’s troops pressed ahead with an offensive to regain territory they lost to rebels trying to topple his regime.
The army has scored major victories in key battlefields in western and central Syria in the past weeks, and is now setting its sights on the country’s largest city, Aleppo, in the north, parts of which have been opposition strongholds.
Despite their seemingly intractable differences, Obama and Putin did express a shared desire to stop the violence in Syria and convene a political conference in Geneva. US officials said they were still aiming to hold the summit next month, though that prospect was looking increasingly unlikely given the deepening violence.
It’s also unclear who would participate in such a meeting or whether the rebels, given their weakened position, would have any leverage if they did.
US officials say Obama’s decision to send the rebels weapons and ammunition for the first time was an attempt to increase their military strength in order to bolster their political bargaining power.
But the American inventory for the rebels is not yet expected to include the high-powered weaponry sought by the opposition, raising questions about whether the deepening US involvement will be effective in changing the situation on the ground.
The White House also announced Monday an additional $300 million in humanitarian aid for Syria and neighboring countries absorbing refugees escaping the violence. The new money brings the total US humanitarian assistance to $800 million, according to the White House.
Obama’s decision to arm the rebels coincided with the White House’s announcement last week that it had definitive evidence of multiple instances of chemical weapons use by Assad’s regime against the opposition. Britain and France have also accused Assad of using the deadly agent sarin, while Russia has publicly questioned the credibility of chemical weapons evidence.
‘‘It’s necessary to refrain from unproven claims by either party,’’ Putin adviser Alexei Kvasov told reporters at the summit Monday. ‘‘We have no evidence proving it.’’
Moscow’s continued support for Assad is based in part on Russia’s deep economic and military ties with his regime. Last month, Russia acknowledged it has agreed to sell Syria advanced S-300 air-defense missiles, which are considered to be the cutting edge in aircraft interception technology.
The Russian president’s divisions with Western leaders on Syria were also on display in his separate meetings with Cameron and France’s president, Francois Hollande.