In the wake of Crimea's vote Sunday in favor of seceding from Ukraine, President Obama said Monday he had expanded sanctions against Russia to show "there are consequences for their actions."

"In recent months, as the citizens of Ukraine have made their voices heard, we have been guided by a fundamental principle: The future of Ukraine must be decided by the people of Ukraine," Obama told reporters in the White House Briefing Room. "That means Ukraine's sovereignty and territorial integrity must be respected and international law must be upheld.

"And so Russia's decision to send troops into Crimea has rightly drawn global condemnation," he added. "And as I told President Putin yesterday, the referendum in Crimea was a clear violation of Ukrainian Constitutions and international law, and it will not be recognized by the international community."

As a result of Sunday's vote, Obama said, he had authorized "a series of measures that will continue to increase the cost on Russia and on those responsible for what is happening in Ukraine," including asset freezes and a ban on travel to the United States for seven Russian and four Ukrainian officials.

The president, who did not take questions, said the sanctions targeted "specific individuals responsible for undermining the sovereignty, territorial integrity and government of Ukraine. We're making it clear that there are consequences for their actions."

He noted he is traveling to Europe next week and Vice President Biden is leaving Monday night for Europe to meet with the leaders of o Poland, Estonia, Latvia and Lithuania--all NATO allies.

"Our message will be clear. As NATO allies, we have a solemn commitment to our collective defense, and we will uphold this commitment," he said.

"Going forward, we can calibrate our response based on whether Russia chooses to escalate or to de-escalate the situation," Obama said. "Now, I believe there's still a path to resolve this situation diplomatically in a way that addresses the interests of both Russia and Ukraine."

Such a path would require Russia withdrawing its forces from Crimea, supporting the deployment of additional international monitors in Ukraine and engaging in negotiations with the Ukrainian government, the president said.

"But throughout this process, we're going to stand firm in our unwavering support for Ukraine," Obama concluded. "And as we go forward, we'll continue to look at the range of ways we can help our Ukrainian friends achieve their universal rights and the security, prosperity and dignity that they deserve."