Special Counsel Robert Mueller’s investigation into possible Russian interference in the 2016 US election is near completion, Acting US Attorney-General Matthew Whitaker says.

“I’ve been fully briefed on the investigation and I look forward to Director Mueller delivering the final report,” he said at a news conference on Tuesday (Australian time).

“Right now the investigation is I think close to being completed and I hope that we can get the report from Director Mueller as soon as possible,” he said.

News of the imminent release of the much-anticipated report coincides with the news that President Donald Trump’s former personal lawyer, Michael Cohen, will testify on February 8 at a closed hearing of the US House of Representatives intelligence committee.

Cohen is set to go to prison in March after pleading guilty campaign finance violations during Mr Trump’s 2016 election campaign, crimes he said he undertook on Mr Trump’s instruction.

The Mueller investigation most recently ensnared a long-time confidant of Mr Trump, political operative Roger Stone, and has led to the conviction of former Trump campaign manager, Paul Manafort.

Mr Mueller has been tight-lipped about when the months of closed-door grand jury sessions and plea deals will conclude, leaving questions over how far into the White House his probe will reach and what will happen to his findings.

Mr Trump’s nominee to fill the attorney general post permanently, William Barr, recently pledged to make public as much of the report as possible, saying Mr Mueller is required to file it confidentially.

Russia denies any wrongdoing in the 2016 election. Trump has repeatedly said he was not involved in any collusion with Russia and has often referred to the probe as a “witch hunt”.

A US federal judge has postponed the February 8 sentencing for Manafort after prosecutors for Mr Mueller’s office accused him of breaching his plea agreement in a parallel case in Washington.

Judge TS Ellis in the Eastern District of Virginia said on Tuesday in a court order that he wanted to delay the sentencing until another judge ruled on whether Manafort had knowingly lied to investigators in breach of his plea deal, noting such a decision “may have some effect on the sentencing decision in this case”.

Manafort pleaded guilty in September 2018 in the Washington case to attempted witness tapering and conspiring against the United States, a charge that covers conduct including money laundering and unregistered lobbying.

He was also separately convicted by a jury in Alexandria, Virginia on eight counts of bank and tax fraud.

-with AAP