U.S. President Donald Trump warned Saturday that his government would stop violent protests over police brutality "cold," following nationwide protests over the death of a black man who died after a white police officer knelt on his neck.

George Floyd, the African American who died on Monday after a Minneapolis police officer knelt on his neck for nearly nine minutes, has become a fresh symbol of police brutality against blacks.

Floyd's death has sparked protests since Tuesday. The demonstrations, some of them violent are now made across the country, including one in Washington on Friday.

"We cannot and must not allow a small group of criminals and vandals to wreck our cities and lay waste to our communities," Trump said in Florida after watching the successful launch of a SpaceX rocket Saturday.

"My administration will stop mob violence. And we'll stop it cold."

How has Trump reacted?

Rather than attempting to bring the nation together, the U.S. president repeatedly asked the states and cities get "much tougher" on demonstrators and warned of using the military stop protests.

Trump first responded in a late-night Thursday tweet saying he will "send in the National Guard" to restore order to Minneapolis.

In a post that Twitter has since hidden and labeled as in violation of the platform's rules about glorifying violence, Trump called protesters as "thugs" and drew a quote from a former Miami police chief, "when the looting starts, the shooting starts."

White Police Chief Walter Headley, who was accused of using racist tactics in his force's patrols of black neighborhoods, used that phrase to "declare war" on Miami's criminals. The chief's tough crackdown also incited mass protests later.

Trump defended his remarks on Friday, claiming ignorance about the origins of the phrase.

Apart from blaming public for misinterpreting his words, Trump Friday also changed the subject by making new attacks on China including stripping Hong Kong's special privileges with the U.S, and cutting ties with the World Health Organization (WHO). 

He mentioned nothing on Floyd's death on Friday's press conference in the White House Rose Garden although reporters kept shouting questions about Floyd and Minnesota.

"Tip: it isn't a press conference when it's a statement delivered without taking questions," New York Times' reporter Maggie Haberman condemned in a tweet after the news conference.

Hundreds of people gathered on Friday afternoon across the street in Lafayette Square Park in Washington and clashed with police.

Trump in several Saturday morning's tweets praising the Secret Service officers who guard the White House for "quickly (coming) down on (protesters), hard - didn't know what hit them" and being "the most vicious dogs, and most ominous weapons, I have ever seen."

Washington Mayor Muriel Bowser responded no Trump, saying there "are no vicious dogs & ominous weapons. There is just a scared man."

"While he (Trump) hides behind his fence afraid/alone, I stand w/people peacefully exercising their First Amendment Right after the murder of #GeorgeFloyd and hundreds of years of institutionalized racism," said Bowser, who is black.

In other tweets on Saturday, Trump continued his blame game.

He also accused Mayor Bowser of refusing to send DC police to help. But the Secret Service said in a statement that "The Metropolitan Police Department and the U.S. Park Police were on the scene."

The president also blamed the extreme left for organizing those violent protests. "The violence and vandalism is being led by Antifa and other radical left-wing groups," he noted.

Trump also slammed some mainstream U.S. news outlets after Minneapolis police officers arrested a CNN reporter live on television without giving any reason on Friday..

"Much more 'disinformation' coming out of CNN, MSDNC, @nytimes and @washingtonpost, by far, than coming out of any foreign country, even combined. Fake News is the Enemy of the People!" Trump wrote.

He again in tweets made threats to protesters saying the "unlimited power of our military" will be unleashed.

(With input from agencies)