America's top law enforcement official refused to appear before Congress Thursday to explain his handling of the special counsel's report on Russian interference, infuriating Democrats who quickly threatened to censure him for contempt.

Attorney General Bill Barr had been grilled a day earlier in the Republican-led Senate, where Democrats accused him of whitewashing the report to protect President Donald Trump.

But he was a no-show at a hearing before the House Judiciary Committee, after its leadership announced it would have lawyers cross-examine him following a round of questioning by the panel's elected members.

If anybody else did that, it would be considered a crime

Barr's absence appeared to antagonise the top congressional Democrat, House Speaker Nancy Pelosi, who accused the attorney general of misleading lawmakers.

"He lied to Congress," Pelosi said, apparently referring to Barr's testimony under oath before lawmakers in April.

In that hearing he claimed not to know whether Mueller supported his controversial memo summarising the Mueller report and that he did not know why members of Mueller's team would be frustrated over the summary.

It emerged on Tuesday however that when Barr said this he was already in possession of a March 27 letter from Mueller outlining the special counsel's frustrations.

"If anybody else did that, it would be considered a crime," Pelosi said. "Nobody is above the law, not the president of the United States, and not the attorney general." 

A contempt motion would open Barr to congressional punishments including fines

Mueller's report, the culmination of a 22-month probe yielding charges or convictions of 34 people and three companies, confirmed that Russian operatives tried to help Trump defeat his Democratic rival Hillary Clinton.

The probe found that Trump's campaign knew of the sabotage attempt and took advantage of the impact on Clinton, but did not deliberately reach out to conspire with the Russians.

The report detailed numerous occasions in which Trump attempted to thwart the investigation, leading to several Democrats calling for his impeachment.

Judiciary Committee chairman Jerry Nadler threatened Barr with contempt of Congress for refusing to comply with a subpoena demanding delivery of the full, unredacted 448-page report.

He also blasted Barr's failure to appear as part of a wholesale obstruction by the Trump administration of a series of Democrat-led inquiries.

"The challenge we face is that the president of the United States wants desperately to prevent Congress, a co-equal branch of government, from providing any check whatsoever to even his most reckless decisions," Nadler told the hearing.

"The system of limited power, the system of not having a president as a dictator, is very much at stake."

The hearing, which adjourned after opening statements by the top lawmakers, was notable for Barr's empty seat.

Democrat Steve Cohen mocked the attorney general's absence, bringing a bucket of Kentucky Fried Chicken to the proceedings.

"Chicken Barr should have shown up today," Cohen said.

Judiciary's top Republican Doug Collins pushed back fiercely, calling the witness-less hearing a "circus" and all but challenging the House leadership to launch impeachment proceedings against Trump.

If the House approves a contempt motion it would open Barr to congressional punishments including fines.