US Attorney General William Barr has assigned a senior federal prosecutor to examine the origins of the Russia investigation, media reports say.
John Durham, the US attorney in Connecticut, has reportedly 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."
He gave no details but said he was gathering a team to look into the origins of the investigation, which was led by special counsel Robert Mueller.
Mr Durham, who has a background in investigating wrongdoing and corruption among public officials, will not be acting as a special counsel in the same way Mr Mueller did, reports say.
But he will be tasked with exploring whether the government acted lawfully and appropriately when collecting intelligence ahead of the 2016 election. Mr Trump and his supporters have often accused the FBI and the Justice Department of illegally monitoring his campaign.
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