WASHINGTON (REUTERS) - President Donald Trump's attorney-general nominee, William Barr, moved closer to a confirmation vote in the US Senate on Thursday (Feb 7), winning approval from a key committee despite Democrats' concerns about how he might handle Special Counsel Robert Mueller's Russia investigation.

Barr is expected to win confirmation in the Republican-controlled chamber as soon as next week, after the Senate Judiciary Committee voted to approve him by a party-line vote of 12 to 10.

A corporate lawyer who previously served as attorney general under Republican President George H.W. Bush in the early 1990s, Barr has been praised by lawmakers from both parties as someone who is deeply familiar with the workings of the Justice Department and does not owe his career to Trump.

If he wins the job, Barr's independence could be put to the test when Mueller wraps up his investigation into the Trump campaign's possible ties to Russia during the 2016 election.

The Republican president has repeatedly criticised the investigation as a "witch hunt" and denies any collusion with Moscow.

Barr criticised the investigation last year in a memo to the Justice Department, but he told the committee in confirmation hearings three weeks ago that he would allow Mueller to conclude his work and said he would make as much of his findings public as possible.

But Barr has refused to promise that he will release the report in its entirety, citing Justice Department regulations that encourage prosecutors not to criticise people who they do not end up charging with criminal behaviour.

Democrats on the committee said they were concerned that Barr's expansive views of presidential power, as outlined in his memo, would lead him to suppress parts of Mueller's report that address whether Trump tried to obstruct the investigation.

"I believe the memo is disqualifying," said Senator Dianne Feinstein, the committee's top Democrat.

Republicans said they were confident Barr would make as much of the report public as possible.

"We need a steady hand at the Department of Justice, and I believe Mr Barr provides that steady hand," said Republican Senator Lindsey Graham, the committee's chairman.

For the time being, Acting Attorney-General Matt Whitaker will remain in charge of the department - and the Mueller investigation.

Whitaker, who was appointed by Trump in November, said last week that the investigation "is close to being completed."

Democrats on the US House of Representatives' Judiciary Committee on Thursday prepared a subpoena to compel Whitaker to testify on Friday, prompting him to say he will not appear unless the subpoena threat is lifted.