HANOI – Hours before his former personal attorney was expected to describe him as a "con man" in bombshell congressional testimony, President Donald Trump broke from a high-stakes summit in Vietnam to fire back, denouncing Michael Cohen as a liar.

"Michael Cohen was one of many lawyers who represented me (unfortunately)," Trump tweeted from Hanoi, site of his second summit with Kim devoted to North Korea's nuclear weapons. "He had other clients also."

Noting that Cohen has been disbarred, the president said "he did bad things unrelated to Trump," and "is lying in order to reduce his prison time."

Trump later retweeted this tweet in the middle of Cohen's testimony.

Cohen's testimony coincides, and has threatened to eclipse, Trump's second summit with North Korean leader Kim Jong Un. As they kicked off their meeting with a brief photo opportunity Wednesday, reporters asked Trump to comment on Cohen.

The president shook his head, but did not respond.

Minutes after the exchange, the White House limited the number of U.S. reporters permitted to witness the next event, a dinner between Trump and Kim. White House press secretary Sarah Sanders said the move was made "due to the sensitive nature of the meetings."

In his earlier posting on Twitter, Trump did not address specific allegations by Cohen, who plans to label the president a "con man," a "cheat," and a "racist" in his testimony before a House committee late Thursday.

The former attorney and fixer plans to say that Trump knew a longtime associate was discussing a WikiLeaks dump of stolen emails related to Hillary Clinton's presidential campaign in 2016, according to Cohen's opening statement obtained by Politico and other media outlets.

Cohen also claims the president implicitly instructed him to lie about a Moscow Trump Tower project negotiated during the 2016 campaign.

The testimony figures to overshadow at least part of the Trump-Kim summit, an event Cohen plans to reference in his testimony.

At one point in his prepared testimony, Cohen cited the college and medical deferments Trump received to avoid military service in the Vietnam War.

"'You think I'm stupid, I wasn't going to Vietnam,'" Cohen quotes Trump as saying.

In his prepared testimony, Cohen adds: "I find it ironic, President Trump, that you are in Vietnam right now."

More:'Conman.' 'Cheat': Cohen set to slam Trump in Wednesday's congressional testimony

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Contributing: John Fritze