U.S. President Barack Obama says the violation of Ukraine's sovereignty and territorial integrity would be deeply destabilizing and urged to respect the independence and sovereignty and borders of Ukraine.

"Any violation of Ukraine's sovereignty and territorial integrity would be deeply destabilizing, which is not in the interest of Ukraine, Russia, or Europe," Obama said in a statement on Ukraine on February 28.

In his words, U.S. Vice President Biden spoke with Ukrainian Prime Minister Arseniy Yatseniuk to assure him that in this difficult moment the United States supports his government's efforts and stands for the sovereignty, territorial integrity and democratic future of Ukraine.

"We will continue to communicate directly with the Russian government," he said.