U.S. Ambassador to Ukraine Geoffrey Pyatt has said it is unacceptable that OSCE Special Monitoring Mission (SMM) faces impediments during its work.

"Unacceptable that Russia supported separatists continue to impede and threaten unarmed OSCE observers," the ambassador wrote on Twitter.

Spokeswoman of the Ukrainian Foreign Ministry Maryana Betsa also criticized Russia.

"We condemn the prevention of SMM activities by the Russian authorized persons. Full freedom of movements needed to carry out monitoring and check ups," she wrote on Twitter.