WASHINGTON (REUTERS) - Investigators in the US Senate and House of Representatives said on Friday (Jan 18) they plan to examine whether US President Donald Trump directed his former lawyer to lie to Congress, prompted by a report by Buzzfeed News.

Leading Democrats in the House of Representatives said they would seek to verify the story, saying that if true it would be evidence of criminal activity by the president.

Buzzfeed, citing two unnamed law enforcement sources, said Trump's former personal lawyer, Michael Cohen, who is going to prison for lying to Congress, told investigators working for Special Counsel Robert Mueller that Trump had directed him to lie about efforts to build a skyscraper in Moscow while he was running for president.

The White House said the story was false. "Look, that's absolutely ridiculous," spokeswoman Sarah Sanders told reporters.

The report said Mueller's office learned of Trump's instructions to Cohen through internal Trump Organisation emails, witness interviews, text messages and other documents, and that Cohen told prosecutors about the directive in an interview.

Trump said on Twitter that Cohen was lying in order to get less prison time, while Trump's lawyer, Rudy Giuliani, said in an email statement, "Any suggestion... that the president counselled his former lawyer Michael Cohen to lie is categorically false."

Mueller's office declined to comment.

Cohen, who once said he was so loyal to Trump that he would "take a bullet" for him, is scheduled to begin a three-year prison sentence in March after pleading guilty to charges that included lying to Congress.

If Trump did tell Cohen to lie, that would constitute criminal activity, said House Judiciary Committee Chairman Jerrold Nadler, who said he would look into the matter.

"Directing a subordinate to lie to Congress is a federal crime," Nadler said on Twitter.

House Intelligence Committee Chairman Adam Schiff said the allegation that Trump may have directed Cohen to lie under oath "is among the most serious to date."

"We will do what's necessary to find out if it's true," he said on Twitter.

Some Senate Intelligence Committee investigators hope to ask Cohen about the BuzzFeed report when he testifies behind closed doors in February, a committee source told Reuters.

He also will face questions about it in testimony before the House Oversight Committee on Feb 7.

NEW EXPOSURE

Legal experts say the allegation exposed Trump to a new level of risk in an investigation that has already resulted in convictions of or guilty pleas from four former campaign aides, including former campaign chairman Paul Manafort.

"It's a seismic event," Andy Wright, an associate White House counsel under former Democratic President Barack Obama, told Reuters.

Cohen adviser Lanny Davis declined to comment on the BuzzFeed report and said Cohen also would not comment.

Cohen's lawyer, Guy Petrillo, did not immediately respond to a request for comment.

Trump denounced Cohen as a "rat" after he began cooperating with investigators while Cohen, whose duties included making payoffs to two women who had affairs with Trump, said on Thursday he regretted giving "my blind loyalty to a man who doesn't deserve it."

Directing or encouraging someone to lie under oath is a crime known as subornation of perjury but the report also raises questions about obstruction of justice and conspiracy.

William Barr, Trump's nominee to be attorney general, said at his confirmation hearing on Tuesday that a president would be committing obstruction if he directed a subordinate to lie under oath. A Justice Department spokeswoman declined to comment.

While the Justice Department has previously concluded that a sitting president cannot be charged while in office, such an allegation, if found true, could fuel impeachment proceedings in Congress.

"Suborning perjury has been a key part of earlier instances where the House has decided to move against a president in the extreme grounds of impeachment," Democratic Senator Tim Kaine told reporters.

Trump repeatedly has denied collusion with Russia and slammed Mueller's investigation as a "witch hunt." Russia also has rejected US intelligence findings that Moscow interfered in US politics in the 2016 election in an effort to boost Trump.

Trump said repeatedly during the presidential campaign that he had no ties or business dealings with Russia. Representatives for the Trump Organisation did not respond to a request for comment on the BuzzFeed report.

Democrats, who took over the US House of Representatives this month, have generally been cautious regarding any talk of impeachment to remove Trump from office although some rank-and-file members have pushed for such a resolution.

It would face an uphill battle in the Senate, where Trump's fellow Republicans have a majority.

Senate Majority Leader Mitch McConnell's office had no comment on the BuzzFeed report but other Republicans said it raised troubling questions.

"Lying to Congress is a whole different issue, obviously, if there was direction to do that. But we've got to hear both sides of the story on this," Senator James Lankford told Reuters.

BuzzFeed on Thursday also reported that Cohen regularly updated Trump's son Donald Trump Jr and his daughter Ivanka Trump, who is now a top White House adviser, about the Moscow project.

A spokesman for Abbe Lowell, a lawyer for Ivanka Trump, said she was minimally involved in the development. Representatives for Trump Jr, who has also testified previously before Congress, did not respond to a request for comment.