Secretary of State Mike Pompeo confirms that he was on the phone along with President Trump and Ukrainian President Volodymyr Zelenskiy, listening to the two leaders speak in a July 25 phone call that has sparked an impeachment inquiry.

In that call, Trump responded to Zelenskiy's appreciation for U.S. defense help by saying, "I would like you to do us a favor though" — and asking the Ukrainian leader for help in finding political ammunition against former Vice President Joe Biden, Trump's potential rival in the 2020 presidential election.

Pompeo discussed the call at a joint news conference in Rome, speaking alongside Italian Foreign Minister Luigi Di Maio during the U.S. diplomat's week-long visit to Italy, the Vatican, Greece and other countries.

In addition to discussing the phone call, Pompeo also criticized the way in which the House impeachment inquiry is being handled — especially Democrats' approach to seeking testimony from State Department officials.

Pompeo said potential witnesses were contacted directly by investigators and told they could not be accompanied by State Dept. attorneys during their testimony — a requirement that he said raises separation of powers concerns for the Trump administration.

"They contacted State Department employees directly — told them not to contact legal counsel at the State Department," Pompeo said in Italy.

Congressional Democrats and Pompeo have been trading accusations that each side is attempting to intimidate or bully witnesses in the impeachment inquiry. On Tuesday, House Democrats postponed what had been expected to be the first of a series of depositions after Pompeo raised objections.

As NPR's Franco Ordoñez reported, that first deposition was expected to occur in a closed session between former U.S. ambassador to Ukraine Marie Yovanovitch and the House Intelligence Committee. That session is now postponed until Oct. 11.

Another closed deposition is scheduled for Thursday, when lawmakers will question another former envoy to Ukraine, Kurt Volker.

NPR's Michele Kelemen contributed to this report.

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