(Reuters) - A U.S. House of Representatives committee will hear closed-door testimony from the intelligence community’s inspector general on Oct. 4, a congressional official said on Friday.

The hearing before the House Intelligence Committee relates to the whistleblower report alleging President Donald Trump abused his office in attempting to solicit Ukraine’s interference in the 2020 U.S. election for his political benefit.

The inspector general, Michael Atkinson, a Trump appointee, determined that the whistleblower’s report was credible.

Atkinson was also concerned that Trump potentially exposed himself to “serious national security and counter-intelligence risks” when he pressed his Ukrainian counterpart to investigate Democratic presidential hopeful Joe Biden and his son during a July 25 phone call, according to a Justice Department legal opinion.

The telephone call between Trump and Ukrainian President Volodymyr Zelenskiy is central to an impeachment investigation announced this week by Nancy Pelosi, speaker of the Democratic-led House of Representatives.

The impeachment inquiry has cast a new pall over Trump’s presidency just months after he emerged from the shadow cast by Special Counsel Robert Mueller’s investigation into whether he colluded with Russia in the 2016 election.

Trump has reacted furiously, arguing he did nothing wrong, and accusing Democrats of launching a politically motivated “witch hunt.”

Trump had ordered $400 million in military aid and foreign assistance for Ukraine to be put on hold a week before the call, and lifted the freeze earlier this month.

Trump denies he pressured Zelenskiy to do anything improper and said he was not using the aid as leverage, but wanted to make sure Ukraine was taking steps to address corruption.