The Republican head of the US Senate judiciary committee says he plans to ask the FBI about a report it launched a probe into whether President Donald Trump has been working on Russia's behalf, suggesting the agency may have gone too far.
"I am going to ask the FBI director - was there a counterintelligence investigation opened up regarding the president as being a potential agent of the Russians? I find it astonishing," Senator Lindsey Graham said on the Fox News Sunday program on Sunday.
"If this really did happen, congress needs to know about it," he added. "How could the FBI do that? What kinds of checks and balances are there?"
The New York Times reported on Friday that the FBI opened the counterintelligence investigation in 2017 after Trump fired then-FBI director James Comey out of concern the president's actions may have presented a threat to national security.
Comey at the time was leading an investigation into Russia's alleged interference in the 2016 US presidential election.
US intelligence agencies have said Moscow tried to tip the election to Trump. Russia has denied interfering, and Trump has said repeatedly there was no collusion between his campaign and Moscow.
The Times reported the counterintelligence probe was sparked in part by growing alarm about Trump's behaviour, including comments he made suggesting he fired Comey over the Russia investigation, which is now being led by Special Counsel Robert Mueller.
Trump rejected the Times story on Saturday, telling Fox News it was "the most insulting article I've ever had written".
Secretary of State Mike Pompeo, who previously served as Trump's CIA director, blasted the Times story, when asked about it on the CBS Face the Nation show.
"The notion that President Trump is a threat to American national security is absolutely ludicrous."
Democratic lawmakers on Sunday said the report underscored the need for legislation to protect the Mueller probe.
Democrats also expressed concern about a report in the Washington Post on Saturday on alleged efforts by Trump to conceal details about his conversations with Putin.
The paper reported that Trump took notes from his interpreter and instructed the person not to discuss the details of his conversation with others.
Reuters could not independently verify details of the Post report.
"When he takes the interpreter's notes and wants to destroy them so no one can see what was said ... it raises serious questions about the relationship between this president and Putin," the Senate's No.2 Democrat, Dick Durbin, said on ABC's This Week.
In his appearance on Fox News on Saturday, Trump denied he was keeping anything under wraps on his meetings with Putin.
Senator Chris Coons, a Democratic member of the judiciary committee, said he plans to press Trump's nominee for attorney general, William Barr, for a pledge to let Mueller complete his work.
Barr is scheduled to testify before the committee on Tuesday and Wednesday. If he is confirmed as attorney general, he would oversee the Russia probe.
He also said Barr must allow Mueller to release a copy of his final report to the public.