The former undersecretary of State and ambassador to NATO under former President George W. Bush on Tuesday denounced President Trump Donald John TrumpBiden on Trump's refusal to commit to peaceful transfer of power: 'What country are we in?' Romney: 'Unthinkable and unacceptable' to not commit to peaceful transition of power Two Louisville police officers shot amid Breonna Taylor grand jury protests MORE for his behavior in the United Kingdom, saying "it's embarrassing to see the American president" act this way.

“This was largely a ceremonial visit," R. Nicholas Burns said on MSNBC. "We expect our president, any president, on a ceremonial visit, to represent all Americans with dignity, with grace, and the president hasn't done that."

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The former NATO ambassador pointed to Trump's criticism of London Mayor Sadiq Khan as an example of how not to act during a state visit to a different country.

"You fly into London, you you criticize the mayor of London, you criticize the opposition leader [Labour Party leader Jeremy Corbyn] and you frankly don't represent the truth about what's happening on the streets of London, these protests," he continued, referring to demonstrations on Tuesday. "This is not the way presidents act overseas."

"Frankly, it's embarrassing to see the American president call out people in this savage, brutal political tirade of criticizing opposition leaders in another allied country," Burns added. "It just makes life difficult for his hosts. How would President Trump appreciate it if any foreign leader came to Washington and began casting bromides about the local politics in the U.S. and criticizing American leaders of both parties?"

Trump has been outspoken during his three-day visit to the U.K., weighing in on issues related to Brexit and taking aim at Khan, the London mayor, on multiple occasions.

He called Khan a "stone cold loser" on Monday after Khan wrote in an op-ed that the United Kingdom was on the “wrong side of history” ahead of Trump's visit.

As many as 250,000 people were expected to attend anti-Trump protests in London on Tuesday. Trump rejected those reports as "fake news" during a press conference with Prime Minister Theresa May Theresa Mary MayAre US-Japan relations on the rocks? Trump insulted UK's May, called Germany's Merkel 'stupid' in calls: report Bolton says Boris Johnson is 'playing Trump like a fiddle' MORE, saying that he's seen thousands of individuals cheering for him.

He also said in the press conference that he had turned down a request from Corbyn to meet, adding that he didn't like how negative he was.