How World Leaders Might Respond to Malaysia Plane Disaster

— -- A day after a Malaysia Airlines jetliner carrying nearly 300 people went down over Eastern Ukraine, President Obama today called the incident an “outrage of unspeakable proportions.”

Obama, for the first time, disclosed that at least one American citizen was killed: Quinn Lucas Schansman. And the president, echoing what U.S. officials said earlier in the day, stated that Flight 17 was brought down by a surface-to-air missile.

“This should snap everybody’s heads to attention,” the president said, vowing to hold “accountable those who committed this outrage.”

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On Capitol Hill, Sen. John McCain alluded to possible consequences Thursday if there is evidence of Russian involvement.

"There'll be hell to pay,” McCain told ABC News.

But how will the world hold the perpetrators “accountable” and what “hell” might be paid? Here are the possible responses from the U.S. and world leaders:

Increase Pressure For A Cease-Fire

This is already happening. Today, Obama said: “Russia, pro-Russian separatists, and Ukraine must adhere to an immediate ceasefire."

He added, "Evidence must not be tampered with."

The president also condemned Russia’s role in the border conflict.

“The violence that’s taken place there is facilitated in part, in large part, because of Russian support. And they have the ability to move those separatists in a different direction,” he said.

Push For An International Investigation

The president called for an international investigation, saying the U.S. has already offered support of the FBI and NTSB.

“Our immediate focus will be on recovering those who are lost [and] investigating exactly what happened,” Obama said.

Other world leaders -- including U.S. allies like German Chancellor Angela Merkel and British Prime Minister David Cameron -- have echoed that call for an investigation.

Impose More Sanctions

Obama did not close the door on imposing additional sanctions against Russia.

“We will continue to make clear that as Russia engages in efforts that are supporting the separatists, that we have the capacity to increase the costs that we impose on them,” he said. “And we will do so not because we're interested in hurting Russia for the sake of hurting Russia, but because we believe in standing up for the basic principle that a country’s sovereignty and territorial integrity has to be respected.”

Any extra sanctions would come on the heels of a new wave of sanctions announced by President Obama on Wednesday.

“These sanctions are significant but they are also targeted, designed to have the maximum effect on Russia while limiting any spillover effects on American companies,” the president added. “The Russian leadership will see once again that its action has consequences.”

The sanctions unveiled earlier this week targeted Russian banks and energy and defense firms.

Get The U.S. Military Involved

This option is not likely -- at least not right now. The president was clear in his remarks at the White House on Friday: “We don’t see a U.S. military role beyond what we’ve already been doing.”

But on Thursday, McCain did suggest the U.S. should provide arms to the Ukrainian military if Russian involvement is proved.

Ask Europe To Take the Lead

The U.S. may encourage European leaders to respond in a stronger manner to any possible Russian involvement in the downing of the Malaysian plane.

“This certainly will be a wake-up call for Europe,” Obama said.