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 on whether Mr Trump tried to end an inquiry into his sacked national security adviser, and about the firing of FBI chief James Comey.
Mr Trump tweeted that the move was the latest action in a “phony story”.
Mr Mueller is leading an FBI inquiry into Russian meddling in the election.
President Trump has repeatedly denied any collusion with Russia, describing the ongoing inquiry as a “witch hunt”.
The latest development was first carried in the Washington Post. Later the New York Times and Wall St Journal reported the story, citing their own sources.
The Washington Post says the decision by Mr Mueller to investigate President Trump’s own conduct is a major turning point in the investigation, which until recently focused on the Russian angle.
Russian President Vladimir Putin has joked about Mr Comey’s testimony, saying the fact that he had admitted leaking details of his conversations with President Trump to the media put him in the same category as US whistleblower Edward Snowden, who was granted asylum in Russia.
“What’s the difference between the FBI head and Mr Snowden then?” Mr Putin asked during a live phone-in with the Russian public in Moscow, adding, “By the way, if he is persecuted in this respect, we will be ready to give him political asylum in Russia too.”
Why is the president being investigated?
The latest media reports say the obstruction of justice investigation began just days after President Trump fired Mr Comey on 9 May.
Mr Comey, who had been leading one of several Russia inquiries, testified to Congress last week that Mr Trump had pressurised him to drop the investigation into former National Security Adviser Michael Flynn.
Mr Flynn was sacked in February for failing to reveal the extent of his contacts with Sergei Kislyak, the Russian ambassador to Washington.
Mr Comey testified under oath that Mr Trump had told him during a private meeting: “I hope you can see your way clear to letting this go, to letting Flynn go. He is a good guy. I hope you can let this go.”
The White House has said the president “has never asked Mr Comey or anyone else to end any investigation, including any investigation involving General Flynn”.
Mr Comey had testified he was “sure” Mr Mueller was looking at whether Mr Trump had obstructed justice.
But Mr Comey also testified that, to his knowledge, the president had not tried to stop the Russia investigation.
However, the Wall St Journal quoted a source as saying that Mr Mueller would examine whether Mr Comey’s sacking was an attempt by the president to alter the course of the investigation.
President Trump said in a TV interview that he had fired the FBI chief because of the “Russia thing”.
Mr Trump reportedly told Russian officials at an Oval Office meeting a day after sacking Mr Comey that his position had now eased.
“I faced great pressure because of Russia. That’s taken off,” Mr Trump said, according to a US official quoted by the New York Times.
Anything else to be examined?
The latest reports also speak of an investigation into possible money laundering among Trump associates.
A former senior official told the New York Times that any collusion between the Trump team and Russian officials would have involved a pay-off, and that there may have been attempts to hide the route of the payments by using offshore banking.
Who is going to be interviewed?
The three names being mentioned in US media are Daniel Coats, the director of national intelligence, Mike Rogers, the head of the National Security Agency, and Richard Ledgett, until recently Mr Rogers’s deputy.
At a Senate panel last week, Mr Coats and Admiral Rogers said they had never felt pressured to interfere in investigations.
The three were not involved in the Trump campaign but may be asked whether Mr Trump sought their help to end the Flynn inquiry.