World leaders vowed a vigorous response to the Islamic State group’s terror spree in Paris as they opened a two-day meeting in Turkey on Sunday, with President Barack Obama calling the violence an “attack on the civilized world” and Russian President Vladimir Putin urging “global efforts” to confront the threat.

But beyond the tough talk and calls for action, there was little indication of how leaders intended to escalate the assault on the extremist group. The attacks in the heart of Europe — combined with earlier incidents in Lebanon and Turkey, as well as the downing of a Russian airliner in Egypt — suggest the Islamic State militants are reaching beyond their base in Iraq and Syria, an expansion the West has feared.

“The skies have been darkened by the horrific attacks that took place in Paris just a day and a half ago,” Obama said shortly after arriving in Antalya, a seaside resort city just a few hundred miles from the Syrian border. He waved off a question from reporters about whether he would authorize additional action against IS.

Turkish President Recep Tayyip Erdogan, the summit host, pledged leaders would produce a “strong message” about fighting international terrorism, though he, too, did not spell out specific steps.

Putin urged nations to pool their efforts to combat terrorism, adding that the fight must respect international law, the U.N. Charter and each nation’s sovereign rights and interests.

“We understand very well that it’s only possible to deal with the terror threat and help millions of people who lost their homes by combining efforts of the entire global community,” Putin said.

While U.S. officials said Obama viewed the attacks in France as an act of war, they cautioned he had no plans to overhaul his strategy for dismantling the Islamic State group and said he remained staunchly opposed to an American ground war in Syria.

The Paris violence ratcheted up the urgency at the previously scheduled Group of 20 summit, an annual meeting of leading rich and developing nations. At least 129 people were killed in Friday’s coordinated attacks around Paris.

In Turkey, five police officers were injured when a suicide bomber blew himself up during a police raid on a suspected IS hideout near the Syrian border. Turkish security forces also rounded up 20 suspected IS militants in and around Antalya before the summit.

The crisis in Syria was already expected to be on the leaders’ agenda given an uptick in diplomatic maneuvering over ways to wind down Syria’s civil war. The conflict has stretched into its fifth year, left more than 250,000 people dead and 11 million displaced, and created a vacuum for the Islamic State and other extremist groups to thrive.

A more immediate option facing leaders was the possibility of France asking for help from its NATO allies. Only once in its 66-year-history — after 9/11 — has NATO’s communal defense obligation been invoked.