US President Donald Trump leaves the White House in Washington D.C., the United States, on Nov. 6, 2019. (Photo by Ting Shen/Xinhua)

 US President Donald Trump said on Friday that he's "not concerned about anything" as first public hearings in his impeachment inquiry were approaching and more transcripts of the inquiry's closed-door depositions were released.

Speaking to reporters outside the White House, Trump said he thinks the testimony "has all been fine."

"I mean, for the most part, I've never even heard of these people. I have no idea who they are. They're some very fine people; you have some Never-Trumpers," the president said. "It seems that nobody has any firsthand knowledge."

The impeachment inquiry, initiated by House Speaker Nancy Pelosi in late September, is looking into White House's alleged efforts in pushing Ukraine to investigate former US Vice President Joe Biden and his son by withholding a military aid approved by Congress.

While Trump has denied any wrongdoing or a "quid pro quo" and the White House has called the impeachment inquiry unfair and illegitimate. House impeachment investigators have conducted a series of closed-doors interviews with former and current Trump administration and released transcripts of depositions by several witnesses.

Trump told reporters that he believes the Democratic-controlled House Intelligence Committee "shouldn't be having" public hearings, the first of which are scheduled for next week.

"This is a hoax. This is just like the Russian witch hunt. This is just a continuation," he said.

The president, in addition to slamming Pelosi and House Intelligence Committee Chairman Adam Schiff, also targeted the anonymous whistleblower whose complaint this summer spurred the impeachment, and the whistleblower's lawyer, Mark Zaid.

"When you look at the lawyer for the whistleblower, I thought it ended when they found out that the lawyer was so compromised. I mean, the lawyer is a bad guy," Trump said.

Zaid, who has fiercely defended his client as some Republicans are calling for the whistleblower's identity to be made public, lashed out at efforts to identify the whistleblower, saying in a tweet on Friday that "protecting whistleblowers is supposed to be nonpartisan issue."

Facebook announced on Friday it will remove from its platform any content that purports to name the whistleblower.

In a statement, a Facebook spokesperson said attempts to unmask the whistleblower violate its policies, and they are "removing any and all mentions of the potential whistleblower's name and will revisit this decision should their name be widely published in the media or used by public figures in the debate."

House Minority Leader Kevin McCarthy tweeted on Friday that Jim Jordan, the top Republican on the House Oversight and Reform Committee, will be placed on the intelligence committee for the duration of the impeachment inquiry.

Jordan, one of Trump's most vocal defenders in the lower chamber, has played a leading role in the impeachment hearings held behind closed doors.

Three House committees leading the impeachment inquiry on Friday released interview transcripts from Lieutenant Colonel Alexander Vindman and Fiona Hill, two national security officials who testified about Trump's contacts with Ukraine.

"Their superiors in the White House have declined to cooperate with the inquiry, but transcripts released today show clearly that individuals close to the President were alarmed by a presidential scheme as illicit and corrupt as a 'drug deal,'" the Democratic chairs said in a joint statement.

According to the transcripts, both Vindman and Hill implicated White House acting Chief of Staff Mick Mulvaney in the Trump administration's alleged effort to press Ukraine for investigating the Bidens.

Mulvaney, viewed as a key witness in the impeachment inquiry because of his involvement in decisions about withholding military aid to Ukraine, defied a House subpoena to testify on Friday, citing White House claims of immunity from compelled congressional testimony.

Former National Security Adviser John Bolton has "personal knowledge" of relevant meetings and conversations "that have not yet been discussed in testimonies thus far" as part of the impeachment inquiry, his lawyer, Charles Cooper, wrote in a letter to lawmakers on Friday.

Cooper, however, made clear that his client is unwilling to testify until a federal court reaches a decision in a legal fight over claims of immunity for White House officials.