WASHINGTON, Nov. 29 (Xinhua) -- U.S. President Donald Trump on Thursday called his former personal lawyer Michael Cohen "a weak person" after he pleaded guilty earlier in the day to lying to Congress about a plan to build a Trump real estate project in Russia.

Cohen is "a weak person" who's lying to get a reduced sentence, Trump said at the White House before leaving for Argentina for the upcoming Group of 20 summit.

During a surprise appearance in federal court in New York Thursday morning, Cohen pleaded guilty to a single count of making false statements to Congress about a Trump Tower development project in Moscow, according to the U.S. Attorney's Office in Manhattan.

Cohen reached the plea deal with special counsel Robert Mueller, who is looking into the alleged Russian interference in the 2016 U.S. presidential election and any potential collusion between the Trump presidential campaign and Moscow.

Federal prosecutors said Cohen lied in a letter submitted in August 2017 to Congressional panels, in which he claimed the Trump Tower project had ended by January 2016, while planning reportedly continued months longer during the presidential campaign.

Cohen said he lied about the timing of the negotiations and other details to be consistent with Trump's "political message."

Responding to Cohen's guilty plea, Trump told reporters that he was never enthused about the project and that he was focused on running for the presidency at that time.

"Even if he was right, it doesn't matter," the president said. "When I run for president, that doesn't mean I'm not allowed to do business. I was doing a lot of different things when I was running."

He said the deal was "very public" and he "wasn't trying to hide anything."

In August, Cohen pleaded guilty to eight counts of campaign finance violations, tax fraud, and bank fraud. But that case was handled by federal prosecutors in New York, rather than the Mueller team. Cohen is scheduled to be sentenced on Dec. 12.

According to the plea agreement, Cohen has been in discussions with Mueller's team, beginning in August and continuing through last week.

Cohen served as a vice-president of the Trump Organization and special counsel to Trump and previously served as co-president of Trump Entertainment.

Trump has recently escalated attacks against the Mueller probe that he has frequently slammed as a "hoax" or "witch hunt." He has denied any wrongdoing or trying to shut down the investigation but has urged Mueller to wrap it up.

Russia has repeatedly denied meddling in the U.S. elections.

Cohen's new guilty plea also comes days after embattled former Trump campaign chairman Paul Manafort was accused of repeatedly lying to investigators after pleading guilty to federal charges related to his work as an unregistered lobbyist for Ukraine -- prior to his time with the Trump campaign.

Prosecutors alleged that Manafort had breached a plea agreement that he signed in September with Mueller, but his attorneys denied that he had lied to federal investigators.