He wrote about this in a series of tweets on Tuesday, Ukrinform reports.
"Russia withdrew its officers from JCCC - a ceasefire implementation tool - right before a massive escalation in ceasefire violations. Ukraine just suffered some of the worst fighting since February, 2017. Decision for peace lies with Russia," the diplomat wrote.
In another post, Volker stressed that the United States expected the political will of the Russian Federation to implement the Minsk accords.
"We are still open for dialogue with Russia and are willing to help facilitate implementation of Minsk agreements, but need political will," Volker said.