The US is to investigate how two ex-FBI heads - both critics of Donald Trump - were subjected to rare, intensive tax audits during his presidency.

The request to check James Comey and Andrew McCabe's cases was made by the Internal Revenue Service (IRS) to the Department of the Treasury.

The news that both men were selected for an uncommon type of audit was first reported in the New York Times.

Individuals are supposed to be selected at random for the audit.

The Times calculated the odds of an individual being selected for the IRS's National Research Program in 2017 at about one in 30,000.

Mr Trump has not commented on the issue.

"The IRS has referred the matter to the Treasury Inspector General for Tax Administration for review," the IRS said in a statement.

The IRS added that this followed "a press inquiry".

According to IRS letters seen by the New York Times, Mr Comey was told that his 2017 return was the subject of a "random" audit. Mr McCabe was told the same about his 2019 return.

On Thursday, Mr McCabe told CNN that referring the matter to "the IG [Inspector General] is the right step, but let's see if the IG moves on it and then makes their findings public".

Mr Comey has so far made no public comment, but told 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."

Mr Trump fired Mr Comey in 2017, the first year of his presidency, as the FBI was investigating alleged links between the Trump campaign and Russia. His dismissal sparked uproar.

Mr McCabe, who became Mr Comey's successor, was dismissed in 2018.