US President Barack Obama this evening condemned rioting in Baltimore, saying there was "no excuse" for the violence, but acknowledged a "slow-rolling crisis" in community policing, especially in treatment of black people.
"We have seen too many instances of what appears to be police officers interacting with individuals - primarily African American, often poor - in ways that raise troubling questions," Mr Obama told reporters at the White House.
"I think there are police departments that have to do some soul-searching. I think there's some communities that have to do some soul-searching. I think we as a country have to do some soul-searching."
Mr Obama was reacting to the violence that erupted in Baltimore after the funeral of Freddie Gray, a 25-year-old black man who died after suffering a spine injury while in police custody.
"This has been a slow-rolling crisis that has been going on for a long time. This is not new. And we shouldn't pretend that it's new," Obama said, referring to tensions in US communities over police actions.
The president said if the country wanted to solve the problem, it needed not only to invest in police training, but also in early education and criminal justice reform.
"That requires more than just the occasional news report or task force," he said.
Earlier, a state of emergency was declared in Baltimore after violent protests over Mr Gray's death.
The US National Guard is to be deployed after 15 police officers were injured when rioters looted businesses and set buildings and vehicles ablaze.
Former Maryland governor and Baltimore mayor Martin O’Malley has cancelled his two-day trip to Ireland to return to the city.
I'm saddened that the City I love is in such pain this night. All of us share a profound feeling of grief for Freddie Gray & his family(1/2)
— Martin O'Malley (@GovernorOMalley) April 27, 2015Firefighters battled several blazes yesterday evening, including a fire under investigation that consumed a church's senior centre under construction in East Baltimore.
Police said looting and assaults against officers continued into the night.
Maryland Governor Larry Hogan declared a state of emergency and sent in the National Guard.
Police made at least 27 arrests and Baltimore schools will be shut today.
Baltimore Mayor Stephanie Rawlings-Blake imposed a citywide curfew beginning tonight, with exceptions for work and medical emergencies.
Mr Gray's death on 19 April reignited a public outcry over police treatment of African Americans that flared last year after the killings of unarmed black men in Ferguson, New York City and elsewhere.
But after several days of peaceful protests over his death, things turned violent yesterday.
Mayor Rawlings-Blake called the looters "thugs" and said they had nothing to do with protests over police brutality.
Looters raided off-licences, pharmacies and a shopping centre.
Rioters smashed car windows outside a major hotel and twice slashed a fire hose while firefighters fought a blaze at a pharmacy that had been looted before it was set on fire.
An Orioles baseball game was cancelled and businesses and train stations shut down in the city.
Mr O'Malley had been booked to address the Byrne Wallace law firm in Dublin on "Ireland's role and place in the world going forward - the view from abroad".
He was also set to deliver a speech on renewable energy to the Sustainable Energy Authority of Ireland and another speech to PricewaterhouseCoopers on the relationship between Ireland and the United States.
He was scheduled to deliver an address to IBM on cybersecurity tomorrow - an industry he supported while governor of Maryland.
