President Trump warned that protesters would have been greeted with 'vicious dogs' and 'ominous weapons' if they breached the fence outside the White House during a demonstration.
In a Twitter thread, Mr Trump said people would have been 'very badly hurt, at least' if the had 'come close' to storming the White House.
The protesters had gathered outside the White House over the killing of African American George Floyd by police in Minneapolis.
The president thanked the Secret Service for doing a 'great job' in their handling of the demonstration.
He tweeted: "They were not only totally professional, but very cool. I was inside, watched every move, and couldn’t have felt more safe. They let the “protesters” scream & rant as much as they wanted, but whenever someone got too frisky or out of line, they would quickly come down on them, hard - didn’t know what hit them.
"The front line was replaced with fresh agents, like magic.
"Big crowd, professionally organized, but nobody came close to breaching the fence. If they had they would have been greeted with the most vicious dogs, and most ominous weapons, I have ever seen.
"That’s when people would have been really badly hurt, at least.
"Many Secret Service agents just waiting for action. “We put the young ones on the front line, sir, they love it, and good practice.
"As you saw last night, they were very cool & very professional. Never let it get out of hand. Thank you! On the bad side, the D.C. Mayor, @MurielBowser, who is always looking for money & help, wouldn’t let the D.C. Police get involved. “Not their job.” Nice!"
Protests have been held across the US following the death of Mr Floyd, who was unarmed when an officer was filmed kneeling on his neck, on Monday.
Curfews have been set in Minneapolis, where there have been fires, looting and violent clashes between demonstrators and police.
