President Barack Obama has warned Russia there will be costs if the country intervenes militarily in Ukraine.
Mr Obama said the US is deeply concerned by reports of military movements by Russia inside Ukraine.
He said any violation of Ukraine's sovereignty and territorial integrity would be destabilising. He said it would violate Russia's commitment to respect Ukraine's borders and would invite global condemnation.
Speaking at the White House, he said the US stands with the world community to affirm there will be costs if an intervention takes place.