US President Donald Trump expressed sympathy for his former campaign manager Paul Manafort and said he would remain "uninvolved" after he attacked Attorney General Jeff Sessions and the US Justice Department in an interview broadcast today.

Trump intensified his criticism of the Justice Department in a Fox News interview taped on Wednesday as the White House grappled to respond to Tuesday's conviction of Manafort on multiple fraud counts and a plea deal struck by Trump's former personal lawyer Michael Cohen that implicated the president.

Trump also said the stock market would crash if he were impeached and attacked Cohen for "flipping" on him.

He reprised a litany of complaints about the Justice Department and the FBI, attacking both without providing evidence they had treated him and his supporters unfairly.

Trump told Fox he respected Manafort for work he had done for prominent Republican politicians, adding that "some of the charges they threw against him, every consultant, every lobbyist in Washington probably does."

The Fox News reporter who interviewed Trump said on Wednesday that Trump told her he would consider pardoning Manafort. But Trump never said he was considering the pardon in the interview that aired on Thursday.

Trump blamed Sessions for what he called corruption at Justice, saying, "I put in an attorney general who never took control of the Justice Department."

However, Trump said he would not interfere in department matters.

"I will stay uninvolved and maybe that's the best thing to do," he said in the Fox interview.

Sessions, a longtime US senator and early supporter of Trump's presidential bid, drew Trump's ire when he recused himself in March 2017 from issues involving the 2016 White House race.

"WHAT KIND OF A MAN?"

That removed him from oversight of the federal special counsel's investigation of Russia's role in the election and whether Trump's campaign worked with Moscow to influence the vote.

"Jeff Sessions recused himself, which he shouldn't have done," Trump said. "He took the job and then he said, 'I'm going to recuse myself.' I said, 'What kind of a man is this?'"

US intelligence agencies have concluded that Russia hacked and leaked Democratic emails during the campaign as part of an effort to tilt the vote in Trump's favor. The Kremlin has denied the allegations and Trump has denied any collusion.

Trump said Manafort and Cohen were charged with matters totally unrelated to his presidential campaign, although Cohen told a federal court in New York that Trump had directed him to arrange payments before the 2016 election to silence two women who said they had affairs withTrump.

Without providing evidence, the Republican president said the campaign finance violations to which Cohen pleaded guilty were not a crime, even though prosecutors and Cohen agreed they were.

Asked if he directed Cohen to make the payments, Trump said only that Cohen made both deals. He attacked Cohen, who once said he was so loyal that he would "take a bullet" for Trump, for agreeing to a plea deal with prosecutors that made Trump look bad.

"It's called flipping and it almost ought to be illegal," he said.

In the Fox News interview, Trump was asked whether he thought Democrats would move to impeach him if they won control of the House of Representatives in November congressional elections.

"I don't know how you would impeach somebody who's done a great job," he said. "If I got impeached, I think the market would crash."