Russian President Vladimir Putin told U.S. President Barack Obama by telephone that Moscow reserves the right to protect its interests and those of Russian speakers in Ukraine, the Kremlin said.
In a statement posted online, the Kremlin said Obama had expressed concern about the possibility of Russian military intervention in Ukraine.
"In response to the concern shown by Obama about the plans for the possible use of Russia's armed forces on the territory of Ukraine, Putin drew attention to the provocative, criminal actions by ultra-nationalists, in essence encouraged by the current authorities in Kiev," the statement said.
"The Russian President underlined that there are real threats to the life and health of Russian citizens and compatriots on Ukrainian territory. Vladimir Putin stressed that if violence spread further in the eastern regions of Ukraine and in Crimea, Russia reserves the right to protect its interests and those of Russian speakers living there."