The US attorney general is stepping up inquiries into the origins of the Russia investigation, working with intelligence chiefs to see how surveillance was conducted and naming a US attorney to oversee the investigation.

The investigation is examining intelligence and surveillance used during the Russia investigation that shadowed Donald Trump’s presidency for nearly two years. William Barr is working with the CIA director, Gina Haspel; director of national intelligence, Dan Coats; and FBI director, Christopher Wray, as part of the inquiry.

Barr tapped John Durham, the US attorney in Connecticut, to lead the inquiry, but Barr remains directly involved in the investigation, which he initiated about three weeks ago, according to a person familiar with the matter. The person could not discuss the matter publicly and spoke Tuesday to the Associated Press on condition of anonymity.

With Durham’s appointment, Barr is addressing a rallying cry of Trump and his supporters, who have accused the justice department and FBI of unlawfully spying on his campaign.

William Barr says 'spying did occur' on Trump campaign during Obama era Read more

Democrats have accused Trump of using the allegations to divert attention from the special counsel Robert Mueller’s findings that Russia aided Trump’s 2016 campaign and that he could not exonerate the president on the question of whether he tried to impede Mueller’s investigation. Mueller did not find a criminal conspiracy between the campaign and the Kremlin.

As he left the White House on Tuesday for a trip to Louisiana, Trump referred to Mueller’s investigation as a “hoax” – as he has frequently done in the past – and said he hadn’t asked Barr to open the inquiry and hadn’t known about it in advance.

“But I think it’s a great thing that he did it,” Trump said. “I am so proud of our attorney general that he is looking into it. I think it’s great.”

Durham’s appointment comes about a month after Barr told members of Congress he believed “spying did occur” on the Trump campaign in 2016. He later said he didn’t mean anything pejorative and was gathering a team to look into the origins of the special counsel’s investigation.

Barr provided no details about what “spying” may have taken place but appeared to be alluding to a surveillance warrant the FBI obtained on a former Trump associate, Carter Page, and the FBI’s use of an informant while the bureau was investigating former Trump campaign foreign policy adviser George Papadopoulos.

Wray said last week that he did not consider court-approved FBI surveillance to be “spying” and said he had no evidence the FBI illegally monitored Trump’s campaign.

Durham’s inquiry, which will focus on whether the government’s methods to collect intelligence relating to the Trump campaign were lawful and appropriate, is separate from an investigation by the justice department’s inspector general. The agency’s watchdog is also examining the Russia inquiry’s origins and Barr has said he expects the watchdog report to be done in May or June.

The former attorney general Jeff Sessions had appointed another US attorney, John Huber, in March 2018 to review aspects of the Russia investigation, following grievances from Republican lawmakers.

The review by Huber, Utah’s top federal prosecutor and an Obama administration holdover, is a “full, complete and objective evaluation” of Republican concerns, Sessions said at the time.

Both the inspector general’s investigation and the inquiry being conducted by Huber are winding down, the person familiar with the inquiries said.

Congressional Republicans have also indicated they intend to examine how the investigation that has shadowed Trump’s presidency began and whether there are any legal concerns.

Durham is a career prosecutor who was nominated for his post as US attorney in Connecticut by Trump. He has previously investigated law enforcement corruption, the destruction of CIA videotapes and the Boston FBI office’s relationship with mobsters.

Durham was unanimously confirmed by the Senate in 2018. At the time, Connecticut’s two Democratic senators, Richard Blumenthal and Chris Murphy, called Durham a “fierce, fair prosecutor” who knows how to try tough cases.

On Tuesday, Blumenthal said Durham was a “talented professional tasked with a very unprofessional and unbecoming mission”.

“This so-called investigation is a politically motivated distraction and threatens to sully his reputation as a straight-shooting, serious, smart prosecutor. It’s a waste of his talent,” Blumenthal said.