A US commentator says police have to stop people who are using race protests to loot and destroy property.
There was more violence overnight in a number of cities following the death of a black man in police custody last week.
George Floyd died after an officer restrained him by holding a knee on his neck - the officer has been charged with murder and is due in court today.
Political commentator and NUIG Law Lecturer, Larry Donnelly, says those using peaceful protest need to be heard.
Riot police clashed with protesters in New York, Chicago, Philadelphia and Los Angeles, firing tear gas and pepper bullets to try to disperse the crowds.
Police vehicles were set on fire and shops were looted in several cities.
The National Guard - the US reserve military force for domestic emergencies - said on Sunday that 5,000 of its personnel had been activated in 15 states and Washington, DC, where crowds once again gathered near the White House, this time lighting fires and throwing stones at riot officers.
Police in Washington DC have fired tear gas at demonstrators who set fire to properties near the White House. They include a historic church, St John's Episcopal Church, known as the church of the presidents, near the White House.
It has emerged that in Friday night's unrest, President Donald Trump was briefly taken by the secret service into an underground bunker at the White House, for his safety.