A spokesman for President Donald Trump’s personal attorney hit back against a Washington Post report that Special Counsel Robert Mueller is investigating the president for possible obstruction of justice.

The Post reported Wednesday evening that Mueller has widened his investigation to include whether Trump obstructed justice, citing five people briefed on the requests and noting that the investigation began after Comey was fired last month.

Mark Carallo, a spokesman for Trump’s attorney Marc Kasowitz, questioned the legality of the leaking information about the investigation, calling it “outrageous, inexcusable and illegal” in a statement to TIME. He did not deny the Post report.

According to the Post, Director of National Intelligence Daniel Coats, Director of National Security Agency Mike Rogers, and Rogers’ former deputy Richard Ledgett agreed to be interviewed by Mueller’s team. Deputy Attorney General Rod Rosenstein appointed Mueller, a former FBI director, to handle the Russia investigation.

Obstruction of justice is essentially defined as intentionally intervening or tampering with an ongoing investigation. However, the key to proving obstruction of justice is that the intervention was done for corrupt purposes.

“If it’s a threat, that makes it a crime. If it’s not a threat — but a request — it could still be a crime if the threat is motivated by a corrupt purpose,”Robert Weisberg, a law professor at Stanford, told TIME last month.

Comey had confirmed during a congressional testimony in March that the FBI was investigating possible Russian interference in the 2016 election, which included possible collusion between the country and Trump associates.

The Post reported June 6 that Coats had told associates Trump had asked him to intervene with Comey when he was still FBI Director to reduce focus on former National Security Adviser Michael Flynn.

The New York Times reported last month that Trump himself had asked Comey to halt any investigation into Flynn, an interaction Comey confirmed during his congressional testimony earlier this month, but Kasowitz denied.

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Write to Alana Abramson at Alana.Abramson@time.com.