As the Minneapolis Police Department’s 3rd precinct building burned early Friday, President Donald Trump lashed out on Twitter, calling the city’s mayor “very weak” and saying that “thugs are dishonoring the memory of George Floyd.” 

In a tweet just before 1 a.m., Trump said he couldn't "stand back & watch this happen to a great American City."

“A total lack of leadership,” Trump tweeted. “Either the very weak Radical Left Mayor, Jacob Frey, get his act together and bring the City under control, or I will send in the National Guard & get the job done right.”

Trump also singled out looters, who have damaged multiple businesses over the past few days. An AutoZone store was set on fire Wednesday night and Target announced it was closing more than 20 locations in the area "until further notice" after one store was ransacked.

"These THUGS are dishonoring the memory of George Floyd, and I won’t let that happen,” Trump tweeted, adding that he had spoken to Gov. Tim Walz and told him that "the Military is with him all the way. Any difficulty and we will assume control but, when the looting starts, the shooting starts. Thank you!"

Twitter later put a public interest notice on that tweet.

"This Tweet violated the Twitter Rules about glorifying violence. However, Twitter has determined that it may be in the public’s interest for the Tweet to remain accessible," the social media company posted.

At a news conference early Friday, Frey said he was unaware of Trump's tweets and asked a reporter to read them to him.

His response: "Weakness is refusing to take responsibility for your actions. Weakness is pointing your finger at somebody else during a time of crisis," the mayor said, striking the lectern at one point. "Donald Trump knows nothing about the strength of Minneapolis. We are strong as hell. Is this a difficult time period? Yes. But you better be damn sure that we’re gonna get through this."

Protests against police brutality and racial discrimination have been ongoing in the wake of the death of Floyd, a black man who died in police custody after a white officer pinned him to the ground under his knee on Memorial Day.

Tensions escalated Thursday night into Friday morning, reaching a boiling point when protesters gained access to the precinct, forcing officers to evacuate and setting several fires, according to the MPD. 

Protests and violence weren't just a problem in Minneapolis. Violence broke out in cities including New York, Denver and Louisville, Kentucky. 

On Wednesday, Trump addressed the death of Floyd for the first time, telling reporters he planned to receive a "full report" on the incident that he described as a "very sad event."

On Thursday, Trump signed an executive order designed – in theory – to make it easier to sue social media companies such as Twitter, days after the site placed a fact check label on two of his tweets.

The order calls for changes in regulations that shield social media companies from legal liability, the Trump administration cannot do that on its own. Those changes can only be made by independent agencies and, ultimately, the courts.

Trump has threatened to somehow punish social media companies for years, claiming they are seeking to suppress conservative views and even trying to influence the 2020 elections.

Trump again slammed Twitter Friday after the website attached another label to one of his tweets. 

"Twitter is doing nothing about all of the lies & propaganda being put out by China or the Radical Left Democrat Party. They have targeted Republicans, Conservatives & the President of the United States. Section 230 should be revoked by Congress. Until then, it will be regulated!"

Contributing: Steve Kiggins, Courtney Subramanian, John Fritze, David Jackson and Jane Onyanga-Omara, USA TODAY