For months, President Obama has spoken about the limits facing the United States in shaping the outcome of some of the world’s most deadly and divisive conflicts, from Syria and Iraq to the dispute between the Ukrainian authorities and pro-Russian separatists.

On Friday, in the aftermath of the downed Malaysian passenger jet over eastern Ukraine, he spoke instead about possibilities.

At a short news conference, Obama said Thursday’s tragedy might persuade European allies and other nations to push more forcefully for an end to the conflict in Ukraine. This week, Europe chose to adopt only modest new economic sanctions against Russia even as the United States ratcheted up the pressure on some of its largest energy and banking firms.

“I think that this certainly will be a wake-up call for Europe and the world that there are consequences to an escalating conflict in eastern Ukraine; that it is not going to be localized, it is not going to be contained,” the president said, noting the particularly deadly toll that the crash took on the Netherlands.

Obama has called British Prime Minister David Cameron and German Chancellor Angela Merkel to discuss the situation in Ukraine and will call other European leaders in coming days, according to Ben Rhodes, deputy national security adviser for strategic communications. European Union officials have given themselves until the end of the month to specify what sanctions they will adopt on various sectors of the Russian economy. Obama is making clear that “those should be severe” if Russia does not shift course, Rhodes said.

Two somewhat similar accidents in the past — the 1983 attack that brought down Korean Air Lines Flight 007 off the Soviet Union’s east coast and the USS Vincennes strike that shot down Iran Air Flight 655 in 1988 — eventually created diplomatic openings. The incidents helped convince bitter enemies that they had more to lose by being in constant conflict than by brokering some sort of detente.

Paul J. Saunders, who served in the State Department under President George W. Bush and is now executive director of the Center for the National Interest, said it appeared unlikely that Russian President Vladimir Putin would significantly change course given that he had encouraged Russian nationalism in Ukraine and had benefited politically at home for doing so. But, he said, “an event like this gives you about the only opportunity you get to pivot on an issue like that.”

“An incident like this highlights for everybody what the dangers are inherent in having conflicts like this without resolution, but the obstacles for getting the two sides together remain,” Saunders added.

The fact that Europe may now be more inclined to take the United States’ side against Russia could exacerbate Putin’s perception that “we’re very much on a glide path toward confrontation,” said Matthew Rojansky, who directs the Woodrow Wilson Center’s Kennan Institute.

“We don’t want to deepen the conflict and make this into an ‘us versus them’ conflict,” Rojansky said. “No one denies that the Russians are part of the solution. They have to be.”

But Rhodes described the current situation as “a pivotal moment” in the push to get Putin to change course. “You can’t help but take that risk, because it’s not as if Russia responds to conciliation, either,” he said.

The president’s words were careful — even lawyerly — as he described who bore the blame for shooting down Malaysia Airlines Flight 17. He noted that the attack took place in a part of Ukraine that is controlled by pro-Russian separatists, where they have shot down as many as three planes in recent weeks. “Moreover,” he said, “we know that these separatists have received a steady flow of support from Russia. This includes arms and training. It includes heavy weapons, and it includes antiaircraft weapons.”

The cautious approach has sparked criticism from some conservatives, who question why the president spoke only briefly about the crash Thursday during an East Coast trip to raise money for Democrats and tout his infrastructure agenda. Fox News’s digital politics editor Chris Stirewalt said on the network’s “The Kelly File” that the president’s “endless talking, his endless fundraising, his endless effort to control every 15 minutes of every news cycle saps him of the ability to speak with authority and resolution when he needs to.”

Obama’s remarks also presented a sharp contrast with comments earlier Friday by U.N. Ambassador Samantha Power, who said during a U.N. Security Council meeting on Ukraine, “Russia can end this war. Russia must end this war.”

Obama remains constrained not only by concerns over alienating Russia, but also by his broader reluctance to commit the United States to further military entanglements. The president said that the nation “stands ready to provide any assistance that is necessary” to support the probe into the plane’s downing, but emphasized that “Russia, these separatists, and Ukraine all have the capacity to put an end to the fighting.”

“You really see in these statements there’s always an effort to thread the needle,” said Nikolas K. Gvosdev, a professor of national security studies at the U.S. Naval War College. “He’s saying, yes, the U.S. should play a role, but he doesn’t want to commit the U.S. to [military] action.” Even as the president seized on the chance for a speedier resolution in Ukraine, there was no sign that he held out even modest hopes that the ongoing warfare between Israelis and Palestinians was coming to an end.

Obama mentioned that he had spoken to Israeli Prime Minister Benjamin Netanyahu on Friday and stressed his support for Israel’s right to defend itself. He told reporters that air sirens in Tel Aviv went off during the call, a sign that another rocket attack was headed toward the city.