Russia is responsible for the “Hot War” in Eastern Ukraine, the newly appointed U.S. special envoy to Ukraine said Sunday.

Kurt Volker, who was appointed by the State Department earlier this month to negotiate an end to more than three years of fighting that has killed 10,000 people, visited Ukraine on the eve of telephone talks between its leader and Russian, German, and French counterparts.

“This is not a frozen conflict, this is a hot war and it is an immediate crisis that we all need to address as quickly as possible,” Volker said in the city of Karamatorsk in the war-torn Donetsk region.

“It is truly a high degree of suffering, there was a high human cost to this conflict and that is another reason why it is so urgent that we address it,” he added.

Volker’s visit followed a particularly bloody week in eastern Ukraine, with at least 11 people killed over the past few days, the most serious flare up of violence in recent months.

The U.S. Congress is set to vote this week on legislation calling for more sanctions against Russia, not only for its meddling last fall in the U.S. election, but also for its 2014 annexation of Ukraine’s Crimean peninsula.