Censor.NET reports citing Reuters.
Volker will be responsible for advancing U.S. interests as set out in the 2015 Minsk agreement and will accompany Tillerson to Kyiv on Sunday, the department said.
Volker was a career diplomat who served as permanent representative to NATO under Republican President George W. Bush and Democratic President Barack Obama. He is currently a foreign policy and national security expert at the McCain Institute for International Leadership at Arizona State University.
"Kurt's wealth of experience makes him uniquely qualified to move this conflict in the direction of peace," Tillerson said. "The United States remains fully committed to the objectives of the Minsk agreements, and I have complete confidence in Kurt to continue our efforts to achieve peace in Ukraine."
During the 2016 presidential campaign, Volker did not sign a letter from more than 90 Republican foreign policy veterans who pledged to oppose Trump, a real estate tycoon with no government or foreign policy experience.
Volker, who was director for European and Eurasian affairs in Bush's National Security Council, said he had concerns that any letter from "national security intelligentsia" could backfire.
"He would actually use it as a bragging right," Volker told Reuters in March. He said he had no intention of working for Trump but wanted to be free to offer advice to any future president, and that such a letter could prompt Trump to hold a grudge.