President Donald Trump is being investigated by special counsel Robert Mueller for possible obstruction of justice, US media reports say.
They say senior intelligence officials will be interviewed about whether Mr Trump tried to end an inquiry into his sacked national security adviser.
Mr Trump’s legal team said the latest leak to the media was “outrageous”.
Mr Mueller is overseeing an FBI inquiry into Russia’s alleged meddling the 2016 US election and any Trump links to it.
President Trump has repeatedly denied any collusion with Russia, describing the ongoing inquiry as a “witch hunt”.
On Wednesday, the Washington Post described the decision by Mr Mueller to investigate President Trump’s own conduct as a major turning point in the investigation, which until recently focused on the Russian angle.
Quoting unnamed officials, the newspaper said Daniel Coats, the director of national intelligence, Mike Rogers, the head of the National Security Agency, and Richard Ledgett, until recently Mr Rogers’ deputy, agreed to be interviewed by investigators.
The questioning could happen as early as this week.
The unnamed officials told the newspaper the obstruction of justice investigation began just days after President Trump fired former FBI director James Comey on 9 May.
Before the sacking, Mr Trump had sought and received assurances from Mr Comey that he personally was not under investigation.
However, Mr Comey has since suggested that Mr Trump attempted to get him to shut down the investigation into his sacked former National Security Adviser Michael Flynn.
Mr Flynn was fired in February for failing to reveal the extent of his contacts with Sergei Kislyak, the Russian ambassador to Washington.
The White House has denied it put pressure on Mr Comey.
Uncharted terrain: Anthony Zurcher, BBC North America reporter
James Comey hinted at it. Washington insiders suspected it. Now US media are reporting it (through anonymous sources, of course).
Donald Trump himself is under direct investigation for obstruction of justice by the special counsel’s office.
Take all those previous assertions by the president that he’s not the target of law enforcement efforts, and throw them out the window.
Mr Trump will surely insist that the inquiry into whether his campaign had ties to Russia is still a hoax perpetrated by Democrats and a hostile media, and that the obstruction allegations are built on that empty foundation.
That may not matter. “It’s not the crime; it’s the cover-up,” may be a hackneyed political saying, but that doesn’t mean it lacks a kernel of truth.
There’s still an open question as to what, exactly, could happen if Mr Mueller does find the president violated the law in acting to disrupt an ongoing investigation.
Could charges be filed? Would it fall on the House of Representatives to act?
It’s all uncharted legal terrain.
If the latest media reports are correct, however, Mr Mueller may be charting a course for the darkness.
President Trump has so far made no comments on the latest report.
However, Mr Trump’s legal team responded angrily.
Mark Corallo, a spokesman for Mr Trump’s lawyer, Marc Kasowitz, said: “The FBI leak of information regarding the president is outrageous, inexcusable and illegal.”