The United States and other Western powers are calling on Russia to exercise restraint in Ukraine.
This, after Russian armored vehicles rumbled across Ukraine's Crimea region, and men described as Russian troops took positions at airports and a coast guard base.
The sudden arrival of men in military uniforms patrolling strategic facilities prompted Ukraine to accuse Russia of "military invasion and occupation."
Secretary of State John Kerry says he's spoken with Russian Foreign Minister Sergey Lavrov -- and that he warned against military moves that could further inflame tensions.
Germany's government says Chancellor Angela Merkel spoke with Russian leader Vladimir Putin, and expressed concern about an escalation in Crimea.
The Kremlin says Putin also spoke with British Prime Minister David Cameron and with the president of the European Union.