A boy wearing a national flag of Ukaine attends a rally against Russia's "intervention" of Crimea, in front of the White House in Washington D.C., the United States, on March 6, 2014. The proposed upcoming referendum in Crimea would violate Ukraine's Constitution and the international law, and any discussion on the future of Crimea should include the Ukrainian government, U.S. President Barack Obama said Thursday. (Xinhua/Yin Bogu)

Demonstrators attend a rally against Russia's "intervention" of Crimea, in front of the White House in Washington D.C., the United States, on March 6, 2014. The proposed upcoming referendum in Crimea would violate Ukraine's Constitution and the international law, and any discussion on the future of Crimea should include the Ukrainian government, U.S. President Barack Obama said Thursday. (Xinhua/Yin Bogu)