U.S. Secretary of State Mike Pompeo has confirmed that he was on the telephone call between President Trump and the Ukrainian president that is the subject of an impeachment inquiry.

"I was on the phone call," Pompeo told reporters in Rome Wednesday during a news conference with his Italian counterpart Luigi Di Maio.

He did not give information about the contents of the call, saying only that he was well-versed in U.S. policy toward Ukraine.

In the July 25 call with the Ukrainian president, Trump prodded him to investigate Trump's Democratic rival Joe Biden and his son, Hunter Biden.

Pompeo is under increasing scrutiny from House Democrats leading impeachment proceedings against Trump. On Tuesday, he pushed back on House demands for interviews with State Department officials about the administration's dealings with Ukraine that are at the center of the inquiry.

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He is currently on a four-nation tour of Europe. He arrived in Rome shortly after U.S officials confirmed he was on the call. 

Pompeo is the first Cabinet official known to have heard Trump press Ukraine's President Volodymyr Zelenskiy to investigate Hunter Biden's ties to a Ukrainian natural gas firm. His participation on the call could indicate that effort to target Biden extended beyond the private lobbying conducted by Trump's personal lawyer, Rudy Giuliani.

Pompeo has said previously that he doesn't believe any State Department official acted inappropriately in contacts with Ukraine's government, and he did not speak to the matter during a brief exchange of pleasantries with reporters aboard his plane.

The response amounts to a confrontation between the executive and legislative branches over impeachment, and could both slow the probe and expose Trump to charges that he is obstructing Congress. In the letter, Pompeo said he would respond to a separate subpoena for him to produce documents related to Ukraine by three House committees by the end of the week.