President Donald Trump speaks with Secretary of State Mike Pompeo during a cabinet meeting in the Cabinet Room at the White House on July 16th, 2019 in Washington, DC.

Secretary of State Mike Pompeo was on the July phone call where President Donald Trump asked his Ukrainian counterpart to investigate Joe Biden and his son, a senior State Department official told NBC News.

The July 25 phone call between Trump and Ukrainian president Volodymyr Zelenskiy and a related whistleblower complaint are now at the center of House Democrats' impeachment inquiry.

Pompeo's involvement in the call — during which Trump told Zelenskiy that Biden's conduct sounded "horrible" to him — was first reported by the Wall Street Journal. It's not unusual for the nation's top diplomat to be on a president's call with a foreign leader, but Pompeo has not acknowledged his involvement.

Pompeo dodged questions about the phone call and the complaint during an interview with ABC's "This Week" on Sept. 22, days before the White House released a summary of the call which showed Trump asking about the Bidens' dealings in Ukraine.

Pompeo had argued against releasing the transcript, saying it would set a bad precedent — never acknowledging he knew exactly what was in the call.

Asked about reports of the substance of the conversation, Pompeo said he wasn't familiar with them and couldn't comment on them. "You just gave me information about a [intelligence community] report, none of which we've seen," he said.

He then turned to the subject of former Vice President Biden, who's running for president.

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"I do think if Vice President Biden behaved inappropriately if he was protecting his son and intervened with Ukrainian leadership in a way that was corrupt, I do think we need to get to the bottom of that," he said. "America can not have our elections interfered with, if that's what took place there."

The House Foreign Affairs Committee subpoenaed Pompeo last week, demanding that he turn over documents related to the phone call.

The panel also sent a separate letter to Pompeo to schedule the depositions of five State Department officials over the next two weeks, including Kurt Volker, who was a special envoy to Ukraine. Volker abruptly quit his post on Friday after he was named in the whistleblower complaint that led to the phone call being revealed.

Pompeo departed Monday evening for a six day European swing that begins in Rome, Italy. He will also travel to Greece, North Macedonia, and Montenegro.