EU warns Americans against non-essential travel to Ukraine . `` There will be costs for any military intervention in Ukraine , '' President Barack Obama says . `` We are strong enough to defend ourselves , '' Americans ambassador says . Ukrainian President Barack Obama to U.S. State Department leaders : Ukraine must avoid an escalation of violence .
U.S. State Department warns Americans against non-essential travel to Ukraine . `` There will be costs for any military intervention in Ukraine , '' President Barack Obama says . `` We are strong enough to defend ourselves , '' Ukrainian ambassador says . Russian President Vladimir Putin to EU leaders : Ukraine must avoid an escalation of violence .