US President Donald Trump has hit back over a news report that he directed his then personal lawyer, Michael Cohen, to lie to Congress.
Buzzfeed News said Mr Trump had instructed Cohen to lie about plans to build a Trump Tower in Moscow. Cohen was convicted over the case last month.
Mr Trump said the lawyer was lying about the Moscow project to "reduce his jail time".
The office of US Special Counsel Robert Mueller also disputed the report.
A spokesman for Mr Mueller - who is investigating alleged Russian interference in the US presidential election and whether Trump campaign figures were complicit - said Buzzfeed's "description of specific statements" and "characterisation of documents and testimony obtained by this office, regarding Michael Cohen's Congressional testimony are not accurate".
Democratic politicians say they will investigate Buzzfeed's allegations.
What does the report say?
Buzzfeed says its report is based on testimony from two unnamed law enforcement officials investigating the matter.
The story alleges Mr Trump received 10 personal updates from Cohen about a plan to build the Moscow tower at a time when Mr Trump denied having any business ties to Russia.
Mr Trump's daughter, Ivanka, and son, Donald Jnr, were also updated, the story alleges.
Mr Mueller has already revealed that Cohen lied about the date the Moscow Trump Tower project ended.
Cohen told Congress talks over the plan had taken place between September 2015 and January 2016 but criminal complaint documents say they lasted until June.
Cohen said the plan had been halted earlier in an attempt to "minimise links between the Moscow Project and Individual 1" during the election campaign. Individual 1 has previously been identified by Cohen as Mr Trump.
Buzzfeed says Cohen has told investigators that Mr Trump "personally instructed him to lie" about the date negotiations ended "in order to obscure Trump's involvement"
The report said Mr Mueller had other evidence, including from interviews with other Trump organisation staff and internal company emails, to corroborate Cohen's version of events.
The report also says Mr Trump allegedly encouraged Cohen to plan a trip to meet Russian President Vladimir Putin during the election campaign.
Cohen was sentenced to 36 months in December after he pleaded guilty to lying to Congress over the Trump Tower plan. He also admitted campaign finance violations and tax evasion.
In court he said his "weakness was a blind loyalty to Donald Trump" - whose "dirty deeds" he had felt compelled to cover up.
A big fuse is lit
Analysis by Anthony Zurcher, BBC News
With the longest government shutdown in history poised to stretch into a fifth week, Washington has become a political powder keg. The report on Thursday night that there is documentary evidence Donald Trump directed his former attorney to lie to Congress just lit a big fuse.
If the Buzzfeed story is substantiated - and it asserts this evidence is already in the hands of Mr Mueller - this would appear to present a strong case for presidential obstruction of justice. Democratic Senator Amy Klobuchar, in a hearing on Tuesday, prompted attorney general nominee William Barr to acknowledge as much.
Already the quiet whispers of impeachment among House Democrats are getting louder. Speaker Nancy Pelosi has been able to tamp down this sentiment so far, but she may be unable - or unwilling - to keep it under wraps much longer.
For almost two years, Mr Mueller's Russia investigation has been a cipher, with details of its activities coming only in opaque legal filings and anonymous accounts of unascertainable veracity.
It seems the time for him to put his cards on the table and end the speculation and parlour-game guessing is rapidly approaching. In fact it's past time, if you ask some Democrats.
What have the Democrats said?
The intelligence committee of the House of Representatives will investigate the claims, says its new chairman, Adam Schiff. He said the allegations against Mr Trump were "among the most serious to date".
The head of the House judiciary committee, Jerrold Nadler, said it would also work to "get to the bottom" of the case.
Some Democrats reacted by calling for impeachment.
Representative Ted Lieu tweeted that the story established a "clear case of Obstruction of Justice, a felony".
Representative for Texas Joaquin Castro said that if the story were true "President Trump must resign or be impeached".
And the Republicans?
The president's response on Twitter mainly retweeted a Fox News reporter's comment that Cohen had been "convicted of perjury and fraud", though the president added "Lying to reduce his jail time!"
The president's current personal lawyer, Rudy Giuliani, issued a statement on Friday saying that "any suggestion from any source that the president counselled Michael Cohen to lie is categorically false".
Earlier, Mr Giuliani told the Washington Post: "If you believe Cohen, I can get you a great deal on the Brooklyn Bridge."
White House Deputy Press Secretary Hogan Gidley told Fox News it was "ludicrous" to give credibility to Buzzfeed, saying its "uncorroborated" story was the kind of fake news the president and his team had to deal with daily. He said that Cohen had been "proven to be a liar".
What is the latest with the Russia investigation?
Mr Mueller's investigation is still ongoing and it is unclear when he will submit his findings to the attorney general. It is up to the attorney general to notify Congress and decide whether the report will be released publicly.
President Trump's nominee for attorney general, William Barr, is currently undergoing confirmation in Congress. He has said he will make as much of the Mueller report public as possible but has not promised to publish it all.
So far Mr Mueller's investigation has led to charges against more than two dozen Russians, as well as several people connected to Mr Trump himself, including his former national security adviser and the former chairman of his election campaign.
A number of them, including Cohen, are known to be co-operating with Mr Mueller's inquiry.
Cohen must report to prison by 6 March, but before that, he has agreed to testify before the House Oversight Committee in February.