U.S. President Donald Trump reportedly told senior Russian officials in a 2017 Oval Office meeting that he was unconcerned about Moscow's alleged interference in the 2016 U.S. election, as leaks about his conduct in office continued in the wake of an explosive whistleblower complaint.

The Washington Post reported on Friday evening that the White House restricted access to the comments, in an echo of the handling of the transcript of the July 2019 phone call between Trump and Ukrainian President Volodymyr Zelensky that has sparked an impeachment inquiry.

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The whistleblower alleges that Trump pressured Zelensky for dirt on a political rival, Joe Biden, using aid money as leverage and that the White House attempted to cover up the incident. The classification of records concerning Trump's interactions with foreign leaders is now a major strand of the scandal.

On a fast-moving day, reports also emerged that Kurt Volker, Trump's special representative for Ukraine, had resigned after being named in the whistleblower complaint and Mike Pompeo, the U.S. secretary of state, has been subpoenaed for documents concerning contact with the Ukrainian government.

'Unconcerned by interference'

The Washington Post reported that during an Oval Office meeting with Russian Foreign Minister Sergei Lavrov and Russian Ambassador Sergey Kislyak in May 2017, Trump said he was unconcerned about interference in the 2016 U.S. presidential election because the United States did the same in other countries.

A summary of the meeting was limited to a handful of officials with the highest security clearances in an attempt to keep the president's comments from being disclosed publicly, former officials told the newspaper.

The meeting was already infamous: Trump reportedly told the Russian officials that firing FBI director James Comey had relieved pressure on him and shared Israeli intelligence with the men. 

Volker quits

CNN reported late on Friday that Volker had stepped down, after initial reports from the State Press, a student-run publication at Arizona State University, which backs a think tank where Volker serves as executive director.

According to the whistleblower complaint from within the intelligence community, Volker spoke with Trump's lawyer Rudy Giuliani to try to "contain the damage" from his efforts to press Ukraine to investigate Biden.

Volker also reportedly set up a meeting between Giuliani and a Zelensky adviser.

Pompeo subpoenaed

The House foreign affairs, intelligence and oversight committees subpoenaed Pompeo after the Trump administration missed a Thursday deadline to provide documents and information about contact with Ukrainian officials, as well as a July 25 telephone call between Trump and Zelensky.

The committees also scheduled depositions for five State Department officials over the next two weeks – four of whom were named in the whistleblower complaint.

The July 25 call is central to the impeachment investigation that Nancy Pelosi, the speaker of the Democratic-led House, announced this week.

More than 300 former national security officials from both Republican and Democratic administrations on Friday endorsed the House's impeachment inquiry, saying they did not prejudge the outcome but wanted to know more facts.

Trump amplifies Biden attacks

Trump's re-election campaign said on Friday it would spend 10 million U.S. dollars airing an ad called "Biden corruption" on television and websites that accuses Democrats of playing politics with the impeachment investigation.

There has been no evidence that former vice president Joe Biden used his position to help his son, Hunter, in the Ukraine matter.

(With input from Reuters)