WASHINGTON — The United States rejected the Crimea secession referendum Sunday as illegal and readied retaliatory penalties against Russia, while shifting sights to deterring possible military advances elsewhere in Ukraine that could inflame the crisis.
As Crimeans voted overwhelmingly to break away from Ukraine and join Russia, President Obama told President Vladimir Putin of Russia that the vote would never be recognized by the United States.
Obama, who spoke by phone with Putin, said the vote violated the Ukrainian constitution and occurred under duress of Russian military intervention. He also said the United States is prepared to impose retaliatory penalties on Russia.
The White House said in a statement that ‘‘no decisions should be made about the future of Ukraine without the Ukrainian government’’ and noted that Russia had rejected the deployment of international monitors in Crimea to ensure the rights of ethnic Russians there were protected.
‘‘Russia’s actions are dangerous and destabilizing,’’ the statement said.
US officials reaffirmed that the Obama administration will, along with the European Union, impose penalties on Russia — including freezing the assets of top officials and private business leaders — if it annexes the strategic region.
They also warned that any Russian moves on east and south Ukraine would be a grave escalation requiring additional responses.
Secretary of State John Kerry called on Moscow to return its troops in Crimea to their bases, pull back forces from the Ukraine border, halt incitement in eastern Ukraine, and support the political reforms that would protect ethnic Russians, Russian speakers, and others in Ukraine that Russia says it is concerned about.
In a call with Foreign Minister Sergei Lavrov of Russia, Kerry urged Russia ‘‘to support efforts by Ukrainians across the spectrum to address power sharing and decentralization through a constitutional reform process that is broadly inclusive and protects the rights of minorities,’’ the State Department said.
Kerry expressed ‘‘strong concerns’’ about Russian military activities in the southern Ukrainian region of Kherson, just north of Crimea, where Russian troops appeared Saturday, and about ‘‘continuing provocations’’ in cities in east Ukraine, the department said.
Kerry ‘‘made clear that this crisis can only be resolved politically and that as Ukrainians take the necessary political measures going forward, Russia must reciprocate by pulling forces back to base and addressing the tensions and concerns about military engagement,’’ the department said.
White House senior adviser Dan Pfeiffer said Russia faces penalties that would hurt its economy and diminish its influence in the world if Putin does not back down. Pfeiffer said the administration is committed to supporting the new Ukrainian government in Kiev ‘‘in every way possible.’’
‘‘President Putin has a choice about what he’s going to do here. Is he going to continue to further isolate himself, further hurt his economy, further diminish Russian influence in the world, or is he going to do the right thing?’’ Pfeiffer said on NBC’s “Meet the Press.’’
US and European officials have said they plan to announce sanctions against Russia, including visa bans and asset freezes, on Monday if Putin does not shift course. But Putin and other Russians show no sign they will back down. They insist they will respect the results of the referendum.