NEW YORK, Sept. 27 - U.S. envoy to Ukraine Kurt Volker resigned on Friday, 1 day after the whistleblower report on President Trump and Ukraine was released, Arizona State University's student newspaper first reported and outlets including CNN confirm.

Volker appears to be the first casualty of an expanding impeachment inquiry into whether Trump has violated rules by asking Ukrainian President Volodymyr Zelenskiy to investigate his political rival ahead of the 2020 presidential election.

Volker was the key U.S. official involved in negotiations over stopping war in eastern parts of Ukraine, and had a tough position towards Russia, which he saw as a force behind fueling the war.

The whistleblower at the heart of a controversy over Trump and Ukraine said that Volker, along with U.S. Ambassador to the EU Gordon Sondland, met with Ukrainian officials a day after Trump's July phone call with Zelenskiy.

According to the whistleblower, Volker and Sondland provided Ukrainian officials with advice on how to "navigate" Trump's demands.

Volker later set up a meeting between Trump’s personal attorney Rudy Giuliani, who had been interested in getting Ukraine to investigate Joe and Hunter Biden, and a Zelenskiy adviser in an effort to get the Biden matter out of official talks.

Volker is scheduled for a deposition on October 3 as part of the House impeachment inquiry and committee investigations into whether Trump jeopardized national security by pressuring Ukraine's president to investigate political rival Joe Biden.

Intelligence Community Inspector General Michael Atkinson found the whistleblower complaint to be credible.

Volker was appointed in 2017 to help resolve the war against Russian-backed separatists in Ukraine’s east. He also directs the McCain Institute, a think tank on Arizona State’s campus. (cnn/ez)