President Obama speaks with Russian President Vladimir Putin, right, Sunday on the sidelines of the Group of 20 summit in Antalya, Turkey. (Kremlin Pool Photo via AP)

— President Obama and Russian President Vladimir Putin met here for the first time since Friday’s terrorist attacks in Paris, struggling to get past their strained personal and political relationships and hoping to craft a coordinated response to the crisis in Syria and the rise of the Islamic State.

Hopes for the meeting were muted. “These relations are what they are. So are the disagreements,” said Russian spokesman Dmitry Peskov. “But there is also the understanding the Russian-U.S. dialogue has no alternative. That’s a hard fact.”

One immediate consequence of the attacks in France has been to raise hard questions about Obama’s often-controversial policy in regard to Syria.

At a meeting of world leaders here, Obama confronted those questions by addressing some of his harshest Syria critics at home and by meeting with Putin, maybe his most formidable antagonist on Syria abroad.

Obama and Putin met Sunday for about half an hour on the sidelines of the two-day Group of 20 summit at this Turkish Mediterranean resort. It was their first conversation since the Paris attacks and a weekend agreement between their governments on trying to forge a diplomatic resolution in Syria’s civil war. The two leaders agreed to support a cease-fire in Syria, followed by U.N.-led negotiations between the regime and opposition forces.

Later, at a contentious news conference after the summit, several reporters prodded Obama in different ways to explain whether he had miscalculated in Syria and misjudged the Islamic State. The president fiercely defended his approach.

“There will be an intensification of the strategy we put forward, but the strategy that we are putting forward is the strategy that ultimately is going to work,” he said, adding that he had urged other leaders at the conference to devote more military and humanitarian resources to responding to the Islamic State, also known as ISIL.

Addressing domestic critics, Obama said most of them have not outlined a specific or alternative strategy to deal with the problem: “Typically the things they suggest need to be done are things that we are already doing.” The one exception, he noted, was the call to dispatch significant numbers of ground troops to Syria and Iraq.

“It is not just my view, but the view of my closest military and civilian advisers, that that would be a mistake — not because our military could not march into Mosul or Raqqa or Ramadi and temporarily clear out ISIL,” he said. “But because we would see a repetition of what we’ve seen before, which is if you do not have local populations that are committed to inclusive governance and who are pushing back against ideological extremes, that they resurface unless we’re prepared to have a permanent occupation of these countries.”

Instead, the United States continues to use airpower as a central element in its military strategy. On Sunday, the U.S. military reported that air attacks struck 116 trucks carrying oil being smuggled by the Islamic State through eastern Syria. The Obama administration has vowed in recent weeks to escalate its airstrikes, particularly on oil smuggling from Syrian fields under Islamic State control. The administration estimates this practice provides the militants with more than $1 million a day in revenue.

U.S. warplanes also hit an Islamic State storage depot near the militants’ de facto capital, Raqqa, in north-central Syria, where French aircraft launched strikes Sunday night in retaliation for the Paris attacks, for which the Islamic State has claimed responsibility.

As civilians continue to flee the conflict in the region, Obama said the United States is prepared to accept additional refugees, though “only after subjecting them to rigorous screening and security checks.”

In the wake of revelations that one of the participants in the Paris attacks may have come to Europe from Syria in early October along with other migrants, several Republican presidential candidates have either called for a total ban on such refugees or suggested that the United States should admit only Syria’s Christians. Obama condemned such ideas in the strongest possible terms, saying, “Slamming the door in their faces would be a betrayal of our values.”

Just before he concluded the news conference, Obama said it was “shameful” that some American politicians would propose favoring one group of migrants over another based on its religious beliefs.

“That’s not American, that’s not who we are,” he said, his voice rising. “We don’t have religious tests to our compassion.”

The administration hopes that the new diplomatic effort will result in Russia joining coordinated air attacks against the Islamic State. But diplomatic success will depend on whether the opposing sides they back in Syria’s separate civil war — with Russia supporting President Bashar al-Assad, and the United States and its allies backing rebel groups trying to oust him — can be persuaded to come to the negotiating table.

“What is different this time and what gives us some degree of hope is that, as I said, for the first time all the major countries on all sides of the Syrian conflict agree on a process that is needed to end this war,” Obama said.

Russia’s relations with the West have been strained since Putin sent heavy weaponry and troops to Ukraine last year. The meeting between Obama and Putin was so impromptu that other leaders milled about in the same lounge area — and a conference center employee attended to a coffee station just a few feet away — as they huddled.

The G-20 summit, normally an annual gathering to discuss global economic issues, has been dominated by the Paris attacks. Obama and Putin met separately with European and Middle Eastern leaders outside larger sessions hosted by Turkish President Recep Tayyip Erdogan.

Obama, who left Turkey for stops in Asia after his news conference, met with his counterparts from Britain, Germany and Italy. France usually participates in the informal group, known as the Quint, but President François Hollande did not attend the summit.

In an interview Monday morning with the BBC, British Prime Minister David Cameron said seven planned terrorist attacks had been foiled in Britain over the past six months. Cameron also said his government would double spending on aviation security and add about 1,900 security and intelligence agents to defend against Islamic State plots.

CIA Director John Brennan said Monday morning that the attacks in Paris were part of a determined effort by the Islamic State to export violence beyond its declared caliphate in Iraq and Syria.

“Not content to limiting its killing fields to Iraq and Syria, ISIL has developed an external operations agenda it is now implementing with lethal effect,” Brennan said in an appearance at a conference in Washington held by the Center for Strategic and International Studies.

He said the attacks in Paris and on a Russian airliner in Egypt “bear the hallmarks of terrorism carried out by the so-called Islamic State . . . an organization of murderous sociopaths.”

Britain also said it would host a donors’ conference next year on humanitarian aid to help the more than 13 million people — more than half of Syria’s population — displaced by the Syrian conflict.

Current U.N. funding for the aid effort has not even reached the levels of last year, when just $3.3 billion was collected in response to a request for $8.4 billion.

International interest in increasing humanitarian aid has risen as tens of thousands of refugees have left Syria and camps in surrounding countries to travel to Europe and beyond.

Greg Jaffe contributed to this report. Eilperin reported from Washington.