Former US president Donald Trump's son-in-law and top White House aide Jared Kushner is due to answer questions Thursday from the House panel investigating last year's assault on the Capitol.

Kushner, the highest-ranking Trump advisor and the first family member to testify so far, is appearing by video link voluntarily and has not been subpoenaed.

He was returning from Saudi Arabia on the day of the January 6 insurrection, and did not spend the night at the White House upon his return to the United States. 

Kushner's appearance caps an intense period of almost daily revelations from the investigation.

It was revealed last week that Ginni Thomas, wife of Supreme Court Justice Clarence Thomas, sent more than two dozen texts pushing wild conspiracy theories and urging then-White House chief of staff Mark Meadows to help overturn the 2020 election.

Kushner's name appeared in a message from Thomas dated November 13, 2020, when she told Meadows: "Just forwarded to yr gmail an email I sent Jared this am... improved coordination now will help the cavalry come and Fraud exposed and America saved."

It also emerged that White House logs given to investigators for the day of the insurrection show a gap of nearly eight hours in Trump's calls, including the period covering the violence.

The committee is investigating whether it has the full record and if Trump communicated that day through phones of aides or personal disposable "burner" phones.

The select committee has also asked for testimony from Kushner's wife, former first daughter Ivanka Trump, who was in the White House on January 6 and pleaded with her father to speak out against the violence, according to reports. 

The White House said on Tuesday it would reject any assertion of "executive privilege" -- which allows presidents to keep certain work-related conversations with aides private -- from Kushner or Ivanka Trump.  

The committee is approaching the end of its investigative phase and is planning public hearings this spring.  

The Department of Justice's investigation of the attack, which left at least five people dead, "has expanded to examine the preparations for the rally that preceded the riot," including those who "assisted in planning, funding and executing" the event, The Washington Post reported.