The U.S. Department of State concerned over escalation of the situation in Ukraine's east, spokesperson John Kirby said on Monday.

"We are deeply troubled by a sharp rise in attacks in eastern Ukraine, particularly the heavy artillery assault on government-controlled Starohnativka. In the last three days, three Ukrainian soldiers have been killed and 35 wounded. Today, Ukrainians reported 127 different separatist attacks, the most since Debaltseve – since the Debaltseve offensive in February. Russia and the separatists it supports cannot simultaneously talk peace and then fight. If they want peace, they must implement the full ceasefire that they agreed to in Minsk," he said at a daily briefing.

Besides, he said on Washington concerns in regard to an arson attack over the weekend that destroyed four OSCE vehicles in Donetsk.

"We call on the separatists to provide security for the OSCE monitoring mission and allow it to do its vital work," Kirby stressed.