US Attorney General William Barr has assigned a senior federal prosecutor to examine the origins of the Russia investigation, ONA reports citing the Associated Press.
John Durham, the US attorney in Connecticut, has been asked to determine whether the collection of intelligence on the Trump campaign was lawful.
President Donald Trump has long called for such an investigation.
He has branded the Russia inquiry a "witch hunt" by his opponents.
Critics of Mr Barr, however, have accused him of acting on behalf of the president rather than in the interests of US justice.
Last month, the attorney general told members of Congress that he believed "spying did occur" on the Trump campaign in 2016, adding: "The question is whether it was adequately predicated. And I'm not suggesting that it wasn't adequately predicated. But I need to explore that."