Michael Cohen, President Donald Trump's former longtime personal attorney and fixer, pleaded guilty in federal court on Thursday to a single count of making false statements to Congress about a project to build a Trump Tower in Moscow.

Cohen's plea marked the first time that Trump and his private business dealings in Moscow were named in open court as part of special counsel Robert Mueller's investigation into Russia's ties to the Trump campaign. Trump had said during the campaign in 2016 that he had no business interests in Russia, but Cohen said in his plea that those business interests were not severed and continued into the summer of 2016.

Prosecutors said Cohen lied in order to minimize links between Trump and his Moscow building project, and to give the false impression that the project had ended before the Iowa caucuses in February 2016.

Cohen, 52, dressed in a navy suit and a white shirt for a surprise appearance in Manhattan court, admitted to making several significant lies to the Senate Select Committee on Intelligence last year about Trump's Moscow project:

• He told Congress the project had ended in January 2016 because of "business reasons." But in fact the project did not end then, and Cohen continued to pursue Russian approval for Trump's project as late as June 2016.

• He told Congress he never agreed to travel to Russia in connection with the project and never considered asking Trump to travel there. In fact, he did agree to travel to Moscow and suggested to Trump that he travel there, too.

• Cohen told Congress he didn't recall any Russian government response or contact about the Russia project. But Cohen admitted he did receive an email from a Russian official and had a phone call with an official about the project, in which he asked for assistance in moving forward on it. The Kremlin had said it never responded to Cohen's request for help.

The plea agreement also indicates that Cohen is cooperating with the special counsel's office.

Read the full charging document

Trump, speaking shortly after Cohen entered his guilty plea on Thursday, called his former attorney a "weak person" who is lying to get a reduced sentence. The president also said his company's effort to build a Trump Tower in Moscow was "a well-known project" that he ultimately decided to scrap.

"So he's lying about a project that everybody knew about," Trump told reporters on the White House South Lawn as he departed for the G-20 summit in Buenos Aires, Argentina.

In July 2016, then-candidate Trump, asked specifically about his financial interests in Russia, said, "I will tell you, right now, zero, I have nothing to do with Russia, yes?"

Trump was set to meet with Russian President Vladimir Putin at the G-20 summit for the first time since they followed up a one-on-one session in Helsinki this summer with a wild press conference. But the president announced on Twitter Thursday that the meeting was off as a result of Russia's aggression toward Ukraine.

Based on the fact that the ships and sailors have not been returned to Ukraine from Russia, I have decided it would be best for all parties concerned to cancel my previously scheduled meeting.... — Donald J. Trump (@realDonaldTrump) November 29, 2018

According to the formal charging document, Cohen briefed "Individual 1," who he identified in open court on Thursday as Trump, about the status and progress of the Moscow project "on more than the three occasions Cohen claimed" to the Senate Select Committee on Intelligence, in addition to briefing the president's family members within the Trump Organization.

Trump's adult children, Donald Trump Jr., Eric Trump and Ivanka Trump, were all senior executives of the Trump Organization at the time. Eric and Donald Jr. are still top executives at the company, having taken over day-to-day control of the business from their father prior to him being sworn in as president.

A second person, who Mueller's team referred to as "Individual 2" in the charging document, appears to be Felix Sater, a Russian-American businessman and former Trump associate with a criminal past.

Sources familiar with Cohen's interview before the House Intelligence Committee last October said there was an extended focus on emails he received in 2015 from Sater about a potential deal to open a Trump Tower in the Russian capital. In the past, Cohen downplayed those conversations, in which Sater bragged about his access to top Kremlin officials, saying it was about "a real estate deal and nothing more."

According to Mueller's charging document, the individual who appears to be Sater had an email conversation with Cohen in May 2016 about arranging a trip to Russia before the 2016 Republican National Convention in July. Cohen was asked if he would meet with a Russian official that June at the St. Petersburg Forum, where Cohen could possibly be introduced to Putin.

Cohen, according to Mueller, met with "Individual 2" to let him know that he would not be traveling to Russia for the forum.

Efforts to build a Trump Tower in Moscow came in the crosshairs of congressional investigators last year as they probed Russian interference in the 2016 presidential election separately from Mueller's investigation. Cohen made appearances before both the House and Senate Intelligence Committees in October 2017.

Earlier this year, The New York Times reported Mueller was scrutinizing the Trump Organization's efforts with regard to the Moscow project. In September 2017, CNN reported on an internal Trump Organization document from October 2015 that it obtained detailing a proposal for a Trump Tower in Russia that would have provided the president’s namesake business with a $4 million upfront fee with no upfront costs.

A source familiar with Cohen's thinking told NBC News that Trump's former attorney is "happy to be cooperating with Mueller" and "has no personal animus toward President Trump."

However, the source said Cohen believes Trump "has changed" since being elected president.

Meanwhile, the source said Cohen is confident the information he provided Mueller, which includes emails, phone calls, and documents, is significant.

Cohen first formally offered information to Mueller on August 7, according to the plea agreement, and went on to have six additional sessions with Mueller's team.

Cohen's lawyer, Lanny Davis, said in a tweet on Thursday that Cohen will continue to work with the special counsel "until the truth is told."

Cohen "this morning reaffirmed what he said last July 2 and told me many times since — that he decided to put his wife, daughter, son and country first. Today he again told the truth and nothing but the truth. @realDonaldTrump called him a liar. Who do you believe?" Davis tweeted.

"I am proud that #robertmueller himself today confirmed that" Cohen has been truthful, Davis continued, "and that truth is relevant and significant. Michael will continue to work with the SC and others until the full truth is told."

1) @MichaelCohen212 this morning reaffirmed what he said last July 2 and told me many times since — that he decided to put his wife, daughter, son and country first. Today he again told the truth and nothing but the truth. @realDonaldTrump called him a liar. Who do you believe? — Lanny Davis (@LannyDavis) November 29, 2018

In a statement, Trump attorney Rudy Giuliani called Cohen a "proven liar who is doing everything he can to get out of a long-term prison sentence for serious crimes of bank and tax fraud that had nothing to do with the Trump Organization."

Cohen was a vice president of the Trump Organization when he left the company in May. A former personal injury lawyer, he began working for the company in 2007 after helping Trump win a fight with the board at his condominium tower near the United Nations. He also owns numerous taxi medallions, which allow drivers to operate yellow cabs in New York.

In August, Cohen pleaded guilty in federal court to eight felony counts of tax evasion, bank fraud and campaign finance violations, including two counts related to hush-money payments Cohen said were made to women at the then-candidate's direction during the 2016 campaign to keep them from discussing affairs they said they had with Trump.

The payments, Cohen said in court at the time, were made for the "principal purpose of influencing" the outcome of the election.

Cohen will be sentenced in both his cases on Dec. 12 in federal court in Manhattan. In Thursday's case, brought by Mueller, Cohen could receive up to six months jail time. In the previous case, it remains to be seen if prosecutors in New York seek to further decrease their recommended sentence of 46 to 63 months.