President Obama spoke for 90 minutes with President Putin about the situation in Ukraine, the White House said.
Obama told Putin that Russia's actions in Ukraine, "would negatively impact Russia’s standing in the international community."
President Obama expressed his "deep concern over Russia’s clear violation of Ukrainian sovereignty and territorial integrity, which is a breach of international law," the White House said.
The United States called on Russia to de-escalate tensions by withdrawing its forces back to bases in Crimea and to refraining from any interference elsewhere in Ukraine.
The Kremlin released their own version of the call, saying Putin asserted that Moscow "reserves the fight" to protect its interests and "drew attention" to the "provocative, criminal actions" of "ultra-nationalists."
Pro-Russia activists recaptured administrative headquarters in the Ukrainian city of Donetsk and flew the Russian flag from its roof.
ITV News' Europe Correspondent describes the tense atmosphere surrounds a central government building in Donetsk .
New footage obtained by ITV News shows Russian troops firing warning shots as Ukrainian soldiers approached during a tense stand-off today.