The Washington Post Wednesday evening reports Mueller "is interviewing senior intelligence officials as part of a widening probe that now includes an examination of whether President Trump attempted to obstruct justice, officials said".
The Washington Post also reported that Mueller's team was looking into conversations that Trump reportedly had with Director of National Intelligence Daniel Coats and National Security Agency Director Mike Rogers about the Russian Federation investigation.
In a statement issued in response to the report, Trump's personal lawyer Marc Kasowitz accused the Federal Bureau of Investigation of leaking the material to the newspaper and called it "outrageous, inexcusable and illegal".
According to the Post's sources, the Justice Department began an investigation into Trump's actions shortly after he dismissed Comey, which the president himself admitted was because of the Russian Federation investigation.
Trump has said he is "100 per cent" willing to testify under oath on Comey meetings and tell the FBI Special Consul Robert Muller that he never asked FBI to stop investigating. According to the Washington Post, that has changed.
The NSA said in a statement that the "NSA will fully cooperate with the special counsel".
Special Counsel Robert Mueller assumed control over that probe and is now scheduling preliminary interviews with several top intelligence officials regarding Trump's actions in office.
"It's my judgment that I was sacked because of the Russian Federation investigation", Comey said.
And on Thursday, the committee will hear testimony from Coats in a classified session - after he refused to say publicly last week whether Trump asked him to pressure Comey to back off Flynn.
A spokesman for Mr Mueller's team declined to comment.
But in a dramatic twist, USA media reports suggest Trump is now under investigation over accusations he tried to influence the FBI inquiry.
Mueller, who was appointed to lead the FBI investigation into Russia's alleged ties to the 2016 U.S. presidential election, briefed Senators on Wednesday on his work.
It is believed that allegations of Trump's obstruction of justice relate to his attempts to encourage Comey to drop an investigation into Mike Flynn, who was forced to resign as Trump's national security adviser earlier this year.
But it is the revelation that the president himself is now under investigation that could prove a seismic development for the nation and Donald Trump's presidency.