Rioters in Toledo, Ohio have attacked police and set fire to property and overturned cars, apparently in protest at a planned neo-Nazi march.
A crowd of about 600 people was involved in the clashes
Police in the US city have made at least 20 arrests, and local officials have declared a state of emergency and issued an all-night curfew.
Reports say a crowd of at least 500 people was involved in the violence.
A small neo-Nazi group of around 20 had gathered in a park to hold a march escorted by police.
The group dispersed when the violence broke out, and the march was cancelled.
The mayor of Toledo, Jack Ford, said the violence was triggered by gang members angry that the neo-Nazi march had been allowed.
Mr Ford said people accused him of protecting the Nazis, and a masked man threatened to kill him when he tried to calm the protesters.
More than 65 people were arrested, and order could be fully restored only after four hours.
Several policemen and fire-fighters were injured in the brawl, which at one point is thought to have involved about 600 people.
"We made about two dozen arrests, but quite frankly could have made a couple of hundred arrests easily," Toledo police chief Michael Navarre said.
The authorities are planning to deploy police in the area for several days to avert further outbreaks of violence.
The National Socialist Movement, a white supremacist group, calls itself "America's Nazi Party".