Special Counsel Robert Mueller's probe into Russian meddling in the 2016 election now includes inquiries into whether President Donald Trump has attempted to obstruct justice.

The investigation had previously been focused on Russian interference, as well as any evidence of financial crimes within the Trump circle, according to the Washington Post.

James Comey, the FBI director who Trump fired in May, had previously told the president three times that he was not under investigation. The Post‘s sources said that changed following Comey's firing.

According to the Post, Director of National Intelligence Dan Coats, National Security Agency Director Mike Rogers, and former deputy NSA head Richard Ledgett all agreed to be interviewed by Mueller's team as early as this week.

The NSA said in a statement that it would cooperate with Mueller's investigation, but did not comment further. The DNI's office and Ledgett declined to comment.

The White House, for its part, expressed distress at the claim that Trump was being investigated.

"The FBI leak of information regarding the president is outrageous, inexcusable, and illegal," said a spokesman for Trump's personal attorney Marc Kasowitz.

Coats, Rogers, and Ledgett will appear voluntarily, but it is unclear whether they will be instructed to invoke executive privilege to avoid answering Mueller's questions. During the Watergate scandal, the Supreme Court found in United States v. Nixon that executive privilege could not be used to withhold evidence in criminal investigations.

According to one source, Mueller sees the obstruction claims as more than just "he said, he said" between Trump and Comey.

He is interested in a number of possible incidents, including one, previously reported on by the Post, in which Trump asked Coats to intervene with Comey to end the investigation into former National Security Adviser Michael Flynn. Trump also asked both Coats and Rogers to disclaim the idea of coordination between his campaign and the Russians.

Mueller has also gathered the memos which Comey created following the now-infamous meeting in which he claims Trump asked him to end his investigation into Flynn.

Mueller has not publicly discussed his work. A spokesman declined to comment when asked by the Post.