WASHINGTON -- A House panel questioned Steve Bannon on Tuesday, aiming to find out President Donald Trump's thinking when he fired FBI Director James Comey, according to a person familiar with what the panel was planning to ask the former White House chief strategist.

The committee also planned to press Bannon on other "executive actions" taken by Trump that have drawn interest from congressional investigators prying into ties between Trump's campaign and Russian operatives, said the person, who wasn't authorized to speak on the record about the closed-door session and spoke to The Associated Press on condition of anonymity.

Those key elements bear directly on the criminal investigation now underway by special counsel Robert Mueller, who is charged with determining if collusion existed between the Trump campaign and Russia and whether the president obstructed justice by firing Comey or by taking other actions to thwart investigators.

As of early Tuesday afternoon, it appeared possible that Bannon could be interviewed all day by the House Intelligence panel -- on par with other top-tier witnesses who have been called before congressional investigators for marathon sessions. Bannon started with the committee at 8 a.m., but questioning did not start until later in the morning.

His interview follows his spectacular fall from power after being quoted in a book that he sees the president's son and others as engaging in "treasonous" behaviour for taking a meeting with Russians during the 2016 campaign.

In Michael Wolff's "Fire and Fury," Bannon accuses Donald Trump Jr., Jared Kushner and former Trump campaign chairman Paul Manafort of essentially betraying the nation by meeting with a group of Russian lawyers and lobbyists who they believed were ready to offer "dirt" on Democratic candidate Hillary Clinton.

More recently, Bannon has said he was not referring to Trump Jr. but rather to Manafort. Wolff stands by his account.

After the book's release, Trump quickly disavowed "Sloppy Steve Bannon" and argued extensively there was no evidence of collusion between his presidential campaign and operatives tied to Russian President Vladimir Putin. Bannon apologized a few days later but was stripped of his job leading the pro-Trump news site Breitbart News.

Bannon last year had largely avoided the scrutiny of congressional investigators, who instead focused much of their energy on trying to secure interviews with top witnesses like Manafort and former national security adviser Michael Flynn.

But Bannon played a critical role in the campaign, the presidential transition and the White House -- all during times now under scrutiny from congressional investigators looking for possible evidence of a connection between Trump's operations and Russia.

Bannon recently retained the same lawyer being used by former Trump chief of staff Reince Priebus and current White House general counsel Don McGahn. Neither Bannon nor his lawyer immediately responded to a request for comment Monday.

The House Intelligence Committee is speeding toward a conclusion of its interviews in its Russia investigation. The final result could be marred by partisan infighting, raising the probability that Republicans on the panel will issue one set of findings and the Democrats will issue their own report.

Bannon's appearance before the committee came as the New York Tiems reported Tuesday that the former Trump adviser has been subpoenaed to testify before a grand jury as part of special counsel Robert Mueller's probe into Russia's possible role in affecting the outcome of the 2016 U.S. presidential election.

- with files from The New York Times