The United States is stepping up pressure on Russia to pull its troops out of Ukraine.
In a phone conservation over the weekend, U.S. President Barack Obama told his Russian counterpart Vladimir Putin that Moscow's continued violation of Ukraine's sovereignty and territorial integrity would "negatively impact Russia's standing in the international community."
Russian soldiers are said to be surrounding several army bases and administrative buildings in the Crimea region, as well as airports and telecommunication centers.
U.S. Secretary of State John Kerry on Sunday denounced Russia for what he called an "incredible act of aggression."
Kerry warned that Russia could be ejected from the Group of eight nations, adding the international community could isolate Russia.
U.S. officials say Kerry will visit Kiev on Tuesday to show Washington's support for the new leadership.
Russia's parliament has already given the green light to Putin to use military force to protect its citizens in Ukraine, defying calls from the international community not to intervene.
Russia has also been staging military exercises involving 150-thousand troops along its border with Ukraine.
The new government in Kiev says it is "on the brink of disaster," and called for the mobilization of its troops in response, accusing Moscow of declaring war.
Ukraine's security officials ordered all armed forces to be put on highest alert, and reserves to be mobilized and trained.
NATO convened an emergency meeting in Brussels on Sunday to discuss the crisis and UN Secretary-General Ban Ki-moon has expressed his "grave concern", urging President Putin to engage in direct dialogue with Ukrainian authorities.
Kim Min-ji, Arirang News.