President Obama spoke to Russian President Vladimir Putin on Thursday about Moscow's military intervention in Ukraine and urged him to find a way to “resolve the situation diplomatically.”

The two leaders spoke for an hour, their first conversation since Saturday, with neither side showing any sign of backing down in the standoff over Crimea.

“President Obama emphasized that Russia's actions are in violation of Ukraine's sovereignty and territorial integrity, which has led us to take several steps in response, in coordination with our European partners,” said the White House in a statement.

“President Obama indicated that there is a way to resolve the situation diplomatically, which addresses the interests of Russia, the people of Ukraine, and the international community.”

The White House said Obama called for Moscow and Kiev to hold “direct talks, facilitated by the international community.” Obama also called for Russian forces to return to their military bases in Crimea and for international monitors to ensure the safety of all Ukrainians.

“President Obama indicated that Secretary Kerry would continue discussions with [Russian] Foreign Minister [Sergei] Lavrov, the government of Ukraine, and other international partners in the days to come to advance those objectives,” the statement added.

The talk came hours after Obama publicly warned Moscow against allowing Crimea to hold a referendum on joining Russia.

“The proposed referendum on the future of Crimea would violate the Ukrainian constitution and violate international law,” Obama said in a statement delivered at the White House.

“Any discussion about the future of Ukraine must include the legitimate government of Ukraine,” he continued. “In 2014, we are well beyond the days when borders can be redrawn over the heads of democratic leaders.”

Russian military forces left their bases in Crimea over the weekend, seizing control of the region. Putin says the move was to protect the ethnic-Russian majority there after Kiev's interim government removed from power former Ukrainian President Viktor Yanukovych, who was backed by Moscow.

But the administration has dismissed Putin's claims, characterizing the incursion as a power grab and promising “costs” if Russia does not stand down.

Crimea’s pro-Russian government decided Thursday to hold a referendum on leaving Ukraine to join Russia.

Earlier in the day, Obama also signed an executive order allowing for targeted sanctions against individuals determined to be “undermining democracy” in Ukraine. The order allows for the State Department to deny visas to those individuals.

The administration though has not shared the names of the individuals targeted for sanctions, and won't say if Putin will be targeted — only that they are poised to act against those responsible for the military action.