US President Donald Trump on Monday threatened that he would deploy the military to quell violent protests against the custodial killing of African-American George Floyd, if the states and cities fail to take necessary actions.

But at the same time, in his address to the nation from Rose Garden of the White House, Trump also said all Americans were "rightly sickened and revolted by the brutal death" of Floyd, and asserted that justice will be served.

Considered to be the worst ever civil unrest in the US in decades, the violent protests have engulfed at least 140 cities across America in the days following the death of Floyd, a 46-year-old man who was pinned to the ground in Minneapolis on May 25 by a white police officer who kneeled on his neck as he gasped for breath.

Trump assured the nation that he is taking actions to stop the violence and restore security and safety in America.

The President said he has mobilized all available federal resources, civilian and military, to stop the rioting and looting, to end the destruction and arson, and to protect the rights of law-abiding Americans, including the Second Amendment rights.

"Today I have strongly recommended to every governor to deploy the National Guard in sufficient numbers that we dominate the streets. Mayors and governors must establish an overwhelming law enforcement presence until the violence has been quelled. If a city or state refuses to take the actions that are necessary to defend the life and proper of their residents, then I will deploy the US military and quickly solve the problem for them," he threatened.

Trump said the country, in the recent days, has been gripped by "professional anarchists, violent mobs, arsonists, looters, criminals, rioters, Antifa and others".

A number of state and local governments have failed to take necessary action to safeguard their residents, he said. "Innocent people have been savagely beaten, like the young man in Dallas, Texas who was left dying on the street, or the woman in upstate New York viciously attacked by dangerous thugs".

"Small business owners have seen their dreams utterly destroyed. New York's finest have been hit in the face with bricks," Trump said.

"Brave nurses who have battled the coronavirus are afraid to leave their homes. A police precinct has been overrun. Here in the nation's capital, the Lincoln Memorial and the World War II Memorial have been vandalized. One of our most historic churches was set ablaze. A federal officer in California, an African-American enforcement hero, was shot and killed," he said.

"These are not acts of peaceful protest. These are acts of domestic terror. The destruction of innocent life and the spilling of innocent blood is an offense to humanity and a crime against God," Trump said.

"I swore an oath to uphold the laws of our nation and that is exactly what I will do. All Americans were rightly sickened and revolted by the brutal death of George Floyd. My administration is fully committed that, for George and his family, justice will be served. He will not have died in vain," he said . Asserting that his administration has not allowed the righteous cries and peaceful protesters to be drowned out by an angry mob, Trump said the biggest victims of the rioting are peace-loving citizens in our poorest communities.

"And as their president, I will fight to keep them safe. I will fight to protect you. I am your president of law and order and an ally of all peaceful protesters," Trump said trying to calm down the situation.

"America needs creation, not destruction; cooperation, not contempt; security, not anarchy; healing, not hatred; justice, not chaos. This is our mission and we will succeed 100 per cent. We will succeed. Our country always wins," the President said.

Describing the violence in Washington DC as a "total disgrace", Trump said he has dispatched thousands and thousands of heavily armed soldiers, military personnel, and law enforcement officers to stop the rioting, looting, vandalism, assaults, and the wanton destruction of property.

"We are putting everybody on warning our 7 pm curfew will be strictly enforced. Those who threaten innocent life and property will be arrested, detained, and prosecuted to the fullest extent of the law," he said.

"I want the organizers of this terror to be on notice that you will face severe criminal penalties and lengthy sentences in jail. This includes Antifa and others who are leading instigators of this violence," Trump said.

The nationwide protests sparked by the killing of Floyd have left at least five people dead. Over 4,000 people have been arrested and curfews imposed in at least 40 cities following the violent protests.