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.