“We’re not going to federalise the Guard at this time.

“But, if necessary, we have further military assets that can be deployed … if the governors and the mayors need it and they can’t get control of the situation,” O’Brien told reporters at the White House, saying law enforcement decisions should rest with governors and mayors.

“We’ll do whatever the governors or mayors need to keep control of their cities,” he added.

Civil unrest has swelled in recent days following Monday’s death of George Floyd, who was shown on video gasping for breath as a white Minneapolis policeman knelt on his neck.

The National Guard said in a statement on Sunday said 5,000 of its soldiers and airmen had been activated in 15 states and Washington, DC, but that “state and local law enforcement agencies remain responsible for security”.

Another 2,000 National Guard troops were ready to activate if needed, the statement said.