According to the White House, Obama reiterated his opposition to Crimea's referendum to determine its country affiliation status, which was deemed "illegal" by Ukraine's government.
"... 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."
Obama called on Putin to embrace a diplomatic resolution to the crisis, and pointed to Ukraine's upcoming elections in May and planned constitutional reform. Russia, Obama urged, should "support the immediate deployment of international monitors to help prevents acts of violence by any groups."
"... 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."
Obama concluded his conversation by telling Putin that Secretary of State John Kerry "continues to be prepared to work together with Foreign Minister Lavrov and the Ukrainian government to find a diplomatic resolution to the crisis."