The OSCE should "immediately" send an observer mission to Ukraine, the US envoy said as the pan-European body met in Vienna on Monday.
"We call today for OSCE observers to be sent immediately to Ukraine," ambassador Daniel Baer said in a speech, released on Monday, to the Organization for Security and Co-operation in Europe.
He said that the OSCE "should make the decision today to move forward with plans and preparation for a monitoring mission immediately".
He said this would "monitor and prevent conflict; ensure the protection of human rights of members of minorities; prevent border conflict; promote respect for territorial integrity; and to maintain peace, stability and security in the region."
His comments were made at a OSCE Preparatory Committee Meeting on Ukraine on Sunday afternoon in Vienna, followed Monday morning by a gathering of the OSCE Special Permanent Council.
Created during the Cold War as a forum for dialogue between East and West and now covering most of the northern hemisphere, the OSCE conducts election monitoring, arms control and conflict prevention activities worldwide.