The Justice Department has reportedly launched a criminal investigation into its own Russia probe that could force top US intelligence officials to testify and may result in charges.

Government sources said Thursday that the inquiry opened by Attorney General William Barr and led by US Attorney John Durham concerning the origins of special counsel Robert Mueller's probe into Russian interference in the 2016 election had transitioned from an administrative review to a criminal investigation.

It is not clear what potential crimes are being investigated, but should the designation of a formal criminal investigation prove true it would gives prosecutors the ability to issue subpoenas, potentially convene a grand jury and compel witnesses to give testimony and bring federal criminal charges.

Among the witnesses likely to face subpoenas are former FBI director James Comey and former CIA head John Brennan.

The Justice Department's inquiry into the origins of special counsel Robert Mueller's probe into Russian interference in the 2016 election has transitioned into a criminal investigation, government sources confirmed Thursday (file photo)

Among the witnesses likely to face subpoenas are former FBI director James Comey (left) and former CIA head John Brennan (right)

Durham, the US attorney from Connecticut, is examining what led the US to open a counterintelligence investigation into Donald Trump's campaign and the roles that various countries played in the US probe.

He is also investigating whether the surveillance methods and intelligence gathering methods used during the investigation were legal and appropriate.

Earlier this week sources told Fox News that the probe had been expanded significantly based on evidence Durham and Barr gathered while on recent covert trips overseas.

The transition from administrative to criminal is likely to elicit concerns that President Trump and his allies may be using the powers of the government to go after their opponents.

The revelation comes as Trump is already facing scrutiny about a potential abuse of power, including a House impeachment inquiry examining whether he withheld military aid in order to pressure the president of Ukraine to launch an investigation of former Vice President Joe Biden and his son Hunter and other theories about the 2016 election.

Barr's decision to have Durham, a widely-respected veteran prosecutor, spearhead the probe could help protect the attorney general from allegations that he is motivated by the president rather than justice.

Attorney General William Barr (left) appointed John Durham (right), the US attorney in Connecticut, to lead the inquiry into the origins of Mueller's probe

The shift from administrative review to criminal investigation is likely to raise concerns that President Donald Trump (pictured Thursday) and his allies may be using the powers of the government to go after their opponents

Mueller's investigation shadowed Trump's presidency for nearly two years and outraged the president, who cast it as a politically motivated 'witch hunt.'

Mueller determined that the Russian government interfered in the 2016 election, but his investigation didn't find sufficient evidence to establish a criminal conspiracy between Trump's campaign and Moscow.

Mueller also examined 10 possible instances of obstruction of justice and has pointedly said he could not exonerate the president.

The Justice Department has said Trump recently made several calls at Barr's request to foreign leaders, including Australian Prime Minister Scott Morrison, to help the attorney general with the Durham investigation.

Barr also traveled with Durham to Italy in August and September, and the two met with Italian intelligence officials to seek information about the activities of FBI agents assigned there, Italian Premier Giuseppe Conte said Wednesday.

Conte said that Italian intelligence officials told Barr that they did not play a role in the events leading up to the Russia investigation.

Ex-Trump aide George Papadopoulos (pictured) has alleged that he was offered Russian 'dirt' on Hillary Clinton in a set-up orchestrated by the CIA or FBI

During one of the meetings - held in a conference room Barr 'could be sure no one was listening in' - the pair reportedly heard a recording from a taped deposition with Joseph Mifsud, the professor widely credited with sparking the counter-intelligence investigation into Trump campaign officials which eventually became wrapped up in Robert Mueller's probe.

Mifsud allegedly offered to give ex-Trump aide George Papadopoulos Russian 'dirt' on Hillary Clinton in a move Papadopoulos suggested was part of a set-up by intelligence agencies.

In the deposition, Misfud told Italian authorities that he feared for his life and needed police protection.

Sources familiar with Durham's investigation told Fox News on Tuesday that the Connecticut attorney is 'very interested' in questioning Brennan, an outspoken critic of Trump who recently called the probe 'bizarre', and former Director of National Intelligence James Clapper.

Brennan and Clapper, both Obama administration officials, were key players during the intelligence community's early assessment about potential Russian interference in the 2016 election.

They were both in office when the Steele Dossier, which was compiled by former British spy Christopher Steele and alleged that Russia had damning information against Trump, was used to justify a secret warrant to surveil ex-Trump adviser Carter Page, one of the main targets in the Russia investigation.

The FBI apparently attempted to obscure the fact that the Clinton campaign and the Democratic National Committee funded the dossier in that warrant application.

If it is true that Durham wants to interview Brennan and Clapper, it would conveniently please the president, who was reported this week by Politico to be 'obsessed' with vengeance on Clapper especially.

Trump was reported to say 'he's an idiot, he's a crook, we ought to investigate him,' about Clapper.

However, Durham's probe appears to have challenges from elsewhere.

The recent expansion came amid concerns over whether the probe has legal or factual basis, multiple sources familiar with the proceedings told NBC News.

Two insiders also claimed that there is tension between the Justice Department and the CIA over what classified documents should be submitted to Durham.