President Donald Trump unleashed his most direct attack yet on his former personal attorney, Michael Cohen, while emphatically denying he knew in advance about his son Donald Jr.'s meeting with Russians in Trump Tower during the 2016 election campaign.

"NO ... I did NOT know of the meeting with my son, Don jr. Sounds to me like someone is trying to make up stories in order to get himself out of an unrelated jam (Taxi cabs maybe?)," Trump tweeted Friday morning, following reports that Cohen has asserted that the president knew about the meeting.

TRUMP TWEET

Trump has repeatedly denied he colluded with Russians to interfere in the 2016 presidential campaign.

Trump's mention of taxi cabs refers to Cohen's reported financial troubles related to the declining value of taxicab medallions in New York. Federal prosecutors in New York City reportedly are eyeing Cohen's ownership and financing of cab medallions.

Trump walked away from shouted questions by reporters about Cohen and a purported former mistress of the president at the end of an appearance at the White House where he was touting a new report of strong U.S. economic growth.

"What do you make of the Cohen tape?" a reporter shouted.

"Is Michael Cohen telling the truth?" another yelled.

"Mr. President, when did you find out about the Karen McDougal allegations?" a journalist asked.

Trump has fumed for days over the news that Cohen had secretly recorded a conversation they had in September 2016 about potentially buying the story of the Playboy model McDougal, who claims she had an affair with Trump. The White House has denied her claims.

Lanny Davis, the lawyer for Cohen who Trump is referring to in his tweet Friday morning, declined to comment. A veteran crisis manager, Davis was President Bill Clinton's special counsel during his scandal-plagued years in the White House.

Trump's lawyer, Rudy Giuliani, and representatives for Hillary Clinton did not immediately respond to CNBC's requests for comment.

Giuliani on Thursday night denied that Trump knew in advance about the Trump Tower meeting, after reports thast Cohen is willing to talk to special counsel Robert Mueller about Trump's alleged foreknowledge.

Giuliani told NBC News that Cohen "can't be believed unless it's corroborated five times."

He added: "I talked to the president about this at length before as well as other witnesses and it's not true. Why would you expect it would be true from someone like Cohen? A lawyer who would tape their own client is a lawyer without any character."

Trump Jr. has repeatedly denied that he told his father in advance about the Trump Tower meeting.

He had agreed to that sitdown so that he could explore a Russian offer of supposedly damaging information on Clinton, Trump's Democratic opponent in the 2016 presidential election. Trump Jr.'s brother-in-law, Jared Kushner, and then-campaign manager Paul Manafort also attended that meeting in early June 2016.

In a first statement to The New York Times following initial reports that the campaign officials met with Russians in Trump Tower, Trump Jr. said "It was a short introductory meeting" in which "we primarily discussed a program about the adoption of Russian children."

It was later revealed that the Russians had offered to provide damaging information on Trump's political opponent during that meeting — and that Trump Jr. had welcomed the possibility of receiving dirt from Russian sources.

One of the Russian attendees, Natalia Veselnitskaya, has since admitted to working for Russian President Vladimir Putin as a Kremlin informant.

A memo sent from Trump's legal counsel to Mueller's team revealed that the president himself had dictated that initial statement to the Times.

Trump's attack on Cohen followed two other tweets on Friday morning, in which he ripped Mueller's team for reportedly examining his Twitter statements as part of a wide-ranging investigation into whether Trump obstructed justice by intimidating witnesses.

Trump tweet Arrived back in Washington

Trump tweet ...., the only Collusion

The new attacks on the special counsel came just days before Manafort is set to begin his trial in federal court.

Mueller's team has charged Manafort with bank fraud and tax crimes related to work he did as a lobbyist for a pro-Russian political party in Ukraine.

The trial is set to begin in U.S. district court in Virginia on Tuesday; another pending case brought by Mueller against Manafort in Washington is scheduled to go to trial in September.

Manafort's longtime business associate, Rick Gates, who had faced similar charges from Mueller, pleaded guilty in February to one count of lying and one count of conspiracy against the United States.