The Obama administration has been accused of criminalising the press, as US lawmakers called for an independent investigator to look into the way the Justice Department conducts cases involving reporters.

President Barack Obama is facing widespread criticism for the aggressive way in which his government investigates leaks, after it emerged that officials had secretly seized phone records from the Associated Press and monitored personal emails of the Fox News reporter James Rosen.

Mr Obama last week directed his Attorney General, Eric Holder, to review the Justice Department’s procedures. Mr Holder is due to report back in July – but his position as the head of the department at the centre of the controversy has led lawmakers to question whether he is the right person to lead the review.

Download the new Independent Premium app Sharing the full story, not just the headlines

“This would be a good time for a special counsel or independent counsel… This is clearly an overreach,” the Republican Senator Lindsey Graham told Fox News. Referring to a case in which the Justice Department obtained the Fox reporter’s private emails, he added: “We’re beginning to criminalise journalism, and I think that should worry us all.”

Concerns about the Obama administration’s tactics were first raised when it emerged that, as part of a separate investigation, officials had secretly seized phone records from the Associated Press.

Another Republican, Tom Coburn, told CBS that Mr Holder’s appointment to head the review was inappropriate. “There’s an inherent conflict of interest in me judging whether I did something and reporting it to the President,” he said. Meanwhile more details have emerged about attempts by Washington to discover who was behind leaks of sensitive information to the press.

A New York Times investigation found that the Obama administration had attempted to trace the origins of two articles about terrorism, written by the same reporters who wrote the Associated Press story that led officials to controversially seize the news agency’s phone records.

But even before the seizure, the government conducted leak investigations into two 2010 articles that also involved Matt Apuzzo and Adam Goldman, the reporters who wrote the Yemen story. One, published in June of that year, included details from a sealed indictment against a man accused of being an Al-Qa’ida operative, while the other piece, published in July 2010 and partly written by the two reporters, concerned the arrest of terror suspects in Norway, according to the New York Times.

Like the Yemen bomb plot piece, AP delayed publication of the Norway story at the government’s request. But law enforcement officials told the New York Times that the disclosures of sensitive information were alarming nonetheless, as they came against the backdrop of continuing intelligence operations overseas.

The paper also said FBI agents had asked the White House and other government agencies last year for communications records showing exchanges with one of its reporters who was writing about Iranian computer attacks.

More damagingly, the aggressive nature of the US government’s leak investigations were underlined last week by details of the way it pursued sources behind a 2009 Fox News article about North Korea by James Rosen.

As part of its probe into the source of the details contained in the article, the Justice Department indicted a State Department analyst and obtained emails from Rosen’s private account, accusing the reporter of being a possible “co-conspirator” in the case, according to court documents. NBC News reported that the Attorney General himself has signed the warrant to access Rosen’s emails.

In the AP case, Mr Holder said he had recused himself from the probe into the Yemen bomb plot leak.

Touching on the case, Senator Graham said: “James Rosen is a lot of things, but not a criminal co-conspirator.”