Russian President Vladimir Putin stressed in a 90-minute phone conversation with U.S. President Barack Obama on Saturday that "Russia reserves its right to protect its interests in eastern Ukraine and Crimea.

Russian President Vladimir Putin stressed in a 90-minute phone conversation with U.S. President Barack Obama on Saturday that "Russia reserves its right to protect its interests in eastern Ukraine and Crimea.

"Vladimir Putin emphasized that, in the case of a further spread in violence in eastern regions (of Ukraine) and Crimea, Russia maintains the right to protect its interests and the Russian-speaking population that lives there," the Kremlin statement said.

Obama told Putin that Russia had committed a clear violation of Ukrainian sovereignty by sending forces into Crimea and warned of consequences, expressing his “deep concern” over Russia’s actions in the past two days and called on Putin to de-escalate tensions by withdrawing his forces back to bases in Crimea and to refrain from any interference elsewhere in Ukraine, the White House said.

Obama also called Russia's actions a "violation of international law" and said they will lead to "greater political and economic isolation," according to the readout of the conversation from the White House Office of the Press Secretary.

"Responding to the concern expressed by Barack Obama about potential military plans over the Ukrainian territory, Putin referred to the criminal nature of the actions of militant nationalists in Ukraine who are encouraged by the new authorities in Kiev," Kremlin statement read.

"Putin noted that Russia reserves the right to protect its interests and the interests of the local population speaking Russian in case the violence spread to the eastern regions of Ukraine and Crimea," it added.

Russian troops took over the Crimea on Saturday after parliament granted Putin approval to invade Ukraine.

Ukrainian Prime Minister Arseny Yatseniuk, leading a government that took power after Moscow's ally Viktor Yanukovych fled a week ago, said Russian military action "would be the beginning of war and the end of any relations between Ukraine and Russia".

Obama also discussed the situation with French President Francois Hollande and Canadian Prime Minister Stephen Harper. According to a statement released by the White House, the leaders agreed to coordinate closely and pledged to work together on a package of support and assistance to help Ukraine.