Attorney General William Barr has given extra protection to the prosecutor he appointed to investigate the origins of the Trump-Russia probe, granting him authority to complete the work without being easily fired.

Mr Barr told The Associated Press on Tuesday he had appointed US Attorney John Durham as a special counsel in October under the same federal statute that governed special counsel Robert Mueller in the original Russia probe.

He said Mr Durham’s investigation had been narrowing to focus more on the conduct of FBI agents who worked on the Russia investigation, known as Crossfire Hurricane.

Under federal regulations, a special counsel can be fired only by the attorney general and for specific reasons such as misconduct, dereliction of duty or conflict of interest. An attorney general must document such reasons in writing.

The FBI in July 2016 began investigating whether the Trump campaign was coordinating with Russia to sway the outcome of the presidential election. That probe was inherited nearly a year later by Mr Mueller, the special counsel who ultimately found insufficient evidence to charge Mr Trump or any of his associates with conspiring with Russia.

But the early months of the investigation, when agents obtained secret surveillance warrants targeting a former Trump campaign aide, have long been scrutinised by the president and other critics of the probe who say the FBI made significant errors.

Barr Election Fraud
Attorney General William Barr (Jeff Roberson/AP)

An inspector general report last year backed up that criticism but did not find evidence that mistakes in the surveillance applications and other problems with the probe were driven by partisan bias.

Mr Barr decided “the best thing to do would be to appoint them under the same regulation that covered Bob Mueller, to provide Durham and his team some assurance that they’d be able to complete their work regardless of the outcome of the election”, he said on Tuesday.

President-elect Joe Biden’s transition team did not immediately comment on the appointment.

The current investigation, a criminal probe, had begun very broadly but has since “narrowed considerably” and now “really is focused on the activities of the Crossfire Hurricane investigation within the FBI”, Mr Barr said.

He said he expected Mr Durham would detail whether any additional prosecutions would be brought, and to make public a report of the investigation’s findings.

In an October 19 order, obtained by The Associated Press, Mr Barr says Mr Durham is authorised “to investigate whether any federal official, employee or any person or entity violated the law in connection with the intelligence, counter-intelligence or law enforcement activities” directed at the 2016 presidential campaigns, anyone associated with the campaigns or the Trump administration.

House Judiciary Committee Chairman, Democrat Jerrold Nadler, said the appointment eroded trust in the Justice Department, and questioned how it was allowed under the special counsel rules.

“And we should not lose sight of the larger picture: in the waning days of the Trump administration, the attorney general has once again used the powers of his office to settle old scores for the president,” Mr Nadler said.

The special counsel rules say the appointed person should be outside of government, but Mr Barr pointed to specific statutes in his memo that would allow him to go around that rule.

Republicans lauded the appointment. Senate Judiciary Chairman Lindsey Graham said it was “obvious the system failed” and he concurred with the appointment of a special counsel to continue the investigation.