U.S. President Barack Obama on Sunday night warned his Russian counterpart Vladimir Putin that the results of the referendum in Crimea would never be recognized by the United States or its allies.
In a phone call which took place after results showed that 95% of Crimea’s residents wanted to join Russia, Obama also hinted at possible additional sanctions on Russia, according to AFP.
Obama told Putin that the vote that violated the Ukrainian constitution.
"President Obama emphasized that the Crimean 'referendum,' which violates the Ukrainian constitution and occurred under duress of Russian military intervention, would never be recognized by the United States and the international community," the White House said in a statement, quoted by AFP.
Joining international condemnation from other world capitals, Obama warned that "Russia's actions were in violation of Ukraine's sovereignty and territorial integrity and that, in coordination with our European partners, we are prepared to impose additional costs on Russia for its actions."
The Kremlin said earlier that the call was initiated by the American side, as relations between Russia and the United States plunged to their lowest point since the Cold War.
Putin told Obama that the referendum was fully legal, "in line with the norms of international law and the UN charter," reported AFP.
"President Obama underscored that there remains a clear path for resolving this crisis diplomatically, in a way that addresses the interests of both Russia and the people of Ukraine," the White House statement added.
"President Obama reiterated that a diplomatic resolution cannot be achieved while Russian military forces continue their incursions into Ukrainian territory and that the large-scale Russian military exercises on Ukraine's borders only exacerbate the tension."
He also stressed that the interim authorities in Ukraine were taking "concrete" steps to help lower tensions over the crisis ahead of May elections.
Russia should support the "immediate" deployment of international monitors to "help prevent acts of violence by any groups," according to the White House statement.
There are questions of coercion in the vote, as Russia effectively militarily occupied Crimea on March 1, with troops taking over the Belbek Airbase. Russia has been consolidating its military hold over the peninsula since, ignoring American condemnation.
U.S. Secretary of State John Kerry spoke with his Russian counterpart Sergei Lavrov on Sunday, warning him that the referendum was not held according to the law, and that America will not recognize the results.
The United States has threatened Russia several times over its incursion in Ukraine, though Moscow has thus far remain unfazed by threats of U.S. sanctions.
Republicans have criticized Obama for his handling of the Ukraine crisis, saying that his “feckless” policy encouraged Putin to invade Ukraine.