The US state of Missouri is sending the National Guard to the town of Ferguson as protests escalate over the police shooting of an unarmed black teenager.
Governor Jay Nixon signed an order to “help restore peace and order and to protect the citizens of Ferguson”.
The decision was made as police clashed with angry crowds shortly before a second night under curfew began.
Police in Ferguson, a suburb of St Louis, said they came under attack and had “no alternative” but to respond.
Capt Ron Johnson said protesters had thrown Molotov cocktails and bottles at security forces, and set up barricades before the five-hour curfew began at midnight (05:00 GMT).
“For those who would claim that the curfew was what led to [the]violence, I will remind you this incident began three and a half hours before the curfew was to have started,” he told journalists in Ferguson on Monday.
Jump media playerMedia player helpOut of media player. Press enter to return or tab to continue.
Police Captain Ron Johnson: “When we saw violent acts… we had to act”
The killing of Michael Brown by a white policeman in a street on 9 August has inflamed racial tensions in the largely black suburb.
Officer Darren Wilson shot the teenager after reportedly stopping him for walking in the street, disrupting traffic.
The governor of Missouri has criticised police for releasing CCTV footage which apparently shows Mr Brown stealing some hours before his death.
Mr Nixon said the release of the footage “appeared to cast aspersions” on the dead man, saying “it made emotions raw”.
But he also condemned the protesters: “These violent acts are a disservice to the family of Michael Brown and his memory and to the people of this community who yearn for justice to be served and to feel safe in their own homes.”