WASHINGTON (AP) — Shouting “Black Lives Matter” and “I can't breathe,” several hundred people converged on the White House for a second straight day Saturday to protest the death of George Floyd in Minneapolis and President Donald Trump's response.

Trump, who earlier belittled the protesters, pledged to “stop mob violence.”

“I stand before you as a friend and ally to every American seeking justice and peace, and I stand before you in firm opposition to anyone exploiting this tragedy to loot, rob, attack and menace," the president said in Florida after watching the launch of a SpaceX rocket. "Healing, not hatred, justice, not chaos are the missions at hand.”

At Lafayette Park, across from the White House, three lines of barricades separated protesters from a loose line of uniformed police officers. At one point, the protesters left the park, chanting as they marched up a nearby street. A block from the White House, they held a moment of silence and brief sit-in.

In a series of tweets earlier Saturday, Trump doubted their allegiance to Floyd’s memory, saying they were “professionally managed.” He offered no evidence to back his assertion, and the president even seemed to invite supporters to make their presence felt: “Tonight, I understand, is MAGA NIGHT AT THE WHITE HOUSE???”

Trump later rejected the suggestion that he was stoking a potential conflict between protesters and his supporters. “I was just asking. But I have no idea if they are going to be here," he said. “MAGA is Make America Great Again. By the way, they love African American people. They love black people.”

At Saturday's demonstration, there was no evidence of a counter-move by Trump supporters.

Trump said he had “watched every move” from inside the executive mansion during Friday's protest and “couldn't have felt more safe” as the Secret Service let the protesters carry on, “but whenever someone ... got too frisky or out of line, they would quickly come down on then, hard — didn't know what hit them.”

The president also criticized the mayors of Washington and Minneapolis.

Trump said Minneapolis Mayor Jacob Frey “is probably a very good person, but he’s a radical, left mayor.” He then described how he watched as a police station in the city was overrun. “For that police station to be abandoned and taken over, I’ve never seen anything so horrible and stupid in my life," Trump said when speaking briefly to reporters at the White House.

He said Minnesota officials have to get tougher with rioters, and that by doing so they would be honoring the memory of Floyd.

The Secret Service said in a statement Saturday that six protesters were arrested in Washington and “multiple” officers were injured. There were no details on the charges or nature of the injuries. A spokesman for U.S. Park Police said their officers made no arrests, but several suffered minor injuries and one was taken to a hospital after being struck in the helmet by a projectile.

Acting Homeland Security Secretary Chad Wolf on Saturday called the protesters “criminals” who committed “acts of violence while hiding behind their First Amendment right of lawful protest.”

Wolf said the Secret Service was “evolving and adapting to the changing nature of the threats they face.”

Floyd is the black man who was being held in handcuffs when he died Monday in Minneapolis after a police officer pressed his knee into his neck for several minutes even after Floyd stopped moving and pleading for air. Protests have erupted in U.S. cities in the days since.

As he tweeted, Trump claimed that many Secret Service agents were “just waiting for action” and ready to unleash “the most vicious dogs, and the most ominous weapons, I have ever seen." His reference to “vicious dogs” potentially being sicced on protesters revisits images from the civil rights movement when marchers faced snarling police dogs and high-pressure fire hoses.

In a news conference Saturday afternoon, Muriel Bowser, mayor of the nation’s capital, called Trump’s remark’s “gross” and said the reference to attack dogs conjures up with the worst memories of the nation’s fight against segregation.

“I call upon our city and our nation to exercise restraint, great restraint, even as the president tries to divide us,” she said. “I feel like these comments are an attack on humanity, an attack on black America, and they make my city less safe.”

In contrast with the president’s tweets, the Secret Service said it “respects the right to assemble and we ask that individuals do so peacefully for the safety of all.”

In protests that stretched into the early hours Saturday, people hurled pieces of bricks, bottles and other objects at Secret Service and Park Police officers who were in riot gear behind barricades around the White House. Protesters at times kicked and punched officers and wrestled over the barricades.

The crowd of hundreds chanted “No justice, no peace” and “Say his name: George Floyd.”

As some in the crowd grew more aggressive, police deployed pepper spray to keep them back and maintain a perimeter of officers around the White House. Fellow demonstrators came to the aid of protesters who were sprayed, their eyes red and puffy, offering bottles of milk and water to splash on their faces.

By the end of the night, the protesters had stolen about 15 barricades and left police to form a line of officers holding riot shields to keep back the swelling crowd. At one point, the protesters were able to gain control of an officer’s shield and set it ablaze before trying to toss it back at the line of officers. Police used a smoke device to stop them.

The protest went on for hours before police declared the gathering “unlawful” and ordered everyone to leave Lafayette Square, a seven-acre public park located directly north of the White House. Dozens of officers pushed forward with their shields and fired off streams of pepper spray at protesters.

“Out of the park or you will be sprayed,” an officer shouted at the crowd.

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AP video journalist Nathan Ellgren contributed to this report.