Separatists in Donbas prevent the OSCE monitors to visit eastern regions, which are under their control now, U.S. Department of State Spokesperson Marie Harf said.

"Russia-supported separatists in eastern Ukraine continue to prevent OSCE monitors from doing their jobs by blocking access to large areas of territory under their control," she said.

According to Harf, yesterday monitors were blocked from entering parts of an area in east of Mariupol.

She said Washington "applauds the efforts of the OSCE to broker a local ceasefire there."

"The Russian-backed separatists signed the Minsk agreements and implementation plan, allowing OSCE monitors access to verify the ceasefire and withdrawal of heavy weapons. This is not happening," the spokesperson stressed.

"We again call for free and unfettered access throughout Ukraine and for the OSCE up to and including the Ukraine-Russia border and urge all sides to work with the OSCE to prevent further violence," Harf said.