The FBI's investigation into the Trump campaign's ties with Russia has extended to a current senior White House official, the Washington Post reported Friday.
The newspaper cited unnamed sources familiar with the probe as saying a current top White House official has been identified as a "significant person of interest," without disclosing the name of the person.
The revelation undercuts President Donald Trump's insistence that his campaign had nothing to do with the Kremlin.
The Russian government is accused by US intelligence of trying to tilt the 2016 election in Trump's favor.
The president's son-in-law Jared Kushner is among those whose contacts with the Russian government have come under scrutiny.
On Thursday, Trump declared himself the victim of the "greatest witch hunt" in American political history and denied allegations of collusion.
"There is no collusion between certainly myself and my campaign, but I can always speak for myself, and the Russians -- zero," Trump told reporters.
The White House on Friday predicted that the investigation would back up Trump's account.
"As the president has stated before -- a thorough investigation will confirm that there was no collusion between the campaign and any foreign entity," said spokesman Sean Spicer.
The White House was rocked by a further revelation Friday, when reports emerged that Trump said his sacking of FBI director James Comey has relieved "great pressure" on him caused by the Russia investigation.
The New York Times reported that Trump told Russian Foreign Minister Sergei Lavrov last week that Comey was a "nut job."
"I faced great pressure because of Russia. That's taken off," Trump told his guest in the Oval Office, the Times said, quoting notes taken at the meeting and read to the paper by a US official.
That flies in the face of the White House's public insistence that Comey's dismissal was not linked to his ongoing investigation.
Spicer offered a new explanation for that firing, saying that Trump had been trying to improve relations with Russia -- and Comey got in the way.
"By grandstanding and politicizing the investigation into Russia's actions, James Comey created unnecessary pressure on our ability to engage and negotiate with Russia," he said.