Washington (AFP) - The Internal Revenue Service said Thursday it had asked for an independent investigation into rare, intrusive audits of two ex-FBI heads who were prominent adversaries of former president Donald Trump.

James Comey, the FBI director until he was sacked by Trump in 2017, and Andrew McCabe, Comey's deputy and temporary replacement, were both subjected to the Internal Revenue Service reviews while the Republican billionaire was in office.

Individuals are supposed to be picked at random for the IRS's National Research Program audits, making the chances of Comey being singled out in 2017 about one in 30,000, while McCabe's odds in 2019 were about one in 20,000.

The revelation, first reported by The New York Times, raised questions over how two men who ran the nation's premier domestic police agency and were seen by Trump as among his most high-profile foes could both have been selected.

Trump sacked Comey in 2017 and then called on him to be arrested for treason, angered by his investigation of the then-president's extensive ties to Russia.

McCabe, who became acting FBI director after Comey's dismissal, was fired by Trump's Justice Department over accusations of lying to investigators that were never followed up with charges.

Trump smeared McCabe, too, again with unfounded treason allegations, and relentlessly pushed for his prosecution.

"I don't know whether anything improper happened, but after learning how unusual this audit was and how badly Trump wanted to hurt me during that time, it made sense to try to figure it out," Comey said in a statement to the Times.

"Maybe it's a coincidence or maybe somebody misused the IRS to get at a political enemy. Given the role Trump wants to continue to play in our country, we should know the answer to that question."

'Political Targeting'

The IRS confirmed in a statement that its head Chuck Rettig -- appointed by Trump in 2018 -- had personally asked a Treasury Inspector General for a review.

"Audits are handled by career civil servants, and the IRS has strong safeguards in place to protect the exam process -- and against politically motivated audits," IRS spokeswoman Jodie Reynolds told AFP.

"It's ludicrous and untrue to suggest that senior IRS officials somehow targeted specific individuals for National Research Program audits."

The referral earned support from lawmakers on both sides of the aisle.

Rep. Richard Neal, the Democratic chairman of the powerful House Ways and Means Committee, said in a statement the "political targeting" of Comey and McCabe marked "a crack in IRS's fragile credibility."

His Republican counterpart Rep. Kevin Brady said he supported "investigating all allegations of political targeting," adding that the IRS should never be used as a weapon against political opponents.

Trump's representatives did not respond immediately to a request for comment, although the Times reported that a spokesman said the ex-president had "no knowledge of this."

Comey's audit lasted more than a year, and he and his wife were found to have overpaid their 2017 federal income taxes and got a $347 refund.

McCabe told the Times he and his wife had paid a small amount they were found to be owing.

"I have significant questions about how or why I was selected for this," he said.