US President Donald Trump's nominee for US attorney general, William Barr, on Tuesday told lawmakers that he believed Russia had meddled in the 2016 US presidential election.

Speaking at his Senate confirmation hearing, Barr said he did not think Special Counsel Robert Mueller's investigation into Russia's interference in the 2016 election and possible collusion between Trump and Moscow was a "witch hunt" as Trump has often described it.

"I don't believe Mr. Mueller would be involved in a witch hunt," Barr said.

Read more: Robert Mueller's US-Russia probe: What you need to know

Barr is expected to win confirmation from the Republican-controlled Senate to serve as the nation's top law enforcement officer, which would put him in charge of Mueller's investigation.

'I will not be bullied'

Barr's comments appeared to pointedly separate himself from Trump's views in what has been seen as an effort to reassure Democrats that he is not a Trump loyalist.

There has been some concert from Democrats over a memo Barr wrote to the US Justice Department before his nomination, in which he criticized part of Mueller's investigation.

Barr told senators on Tuesday he was only trying to warn Justice Department officials against "stretching a statute" to conclude that the president had obstructed justice.

"I will not be bullied into doing anything that I think is wrong, whether it be by editorial boards, Congress or the president," Barr told senators on the Judiciary Committee.

Barr who is 68 years old and partially retired said: "I feel that I'm in a position in life where I can do the right thing and not really care about the consequences."

Mueller investigation 'vitally important'

Barr told lawmakers he would consult with ethics officials on whether he would need to recuse himself because of the memo, but that the decision would ultimately be his. He also revealed having discussed Mueller with Trump during a meeting in 2017 when Barr declined to join his legal team.

Mueller is due to submit a final report to the attorney general, prompting concern from some Democrats that the Trump administration will try to meddle with his findings.

Barr said he would not let Trump make changes to the report and would make public as many of Mueller's findings as possible.

Barr said "it is vitally important" that Mueller is allowed to complete his investigation and that Congress and the public should learn the results.

He also insisted that Trump never sought any promises, assurances or commitments from him before selecting him to be the country's chief law enforcement officer.

law/jil (AP, Reuters)