Police came under "heavy gunfire" and 31 people were arrested, authorities said on Tuesday, during racially charged protests in Ferguson, Missouri sparked by the fatal shooting of an unarmed black teenager by a white policeman 10 days ago.
"Not a single bullet was fired by officers despite coming under heavy attack (on Monday night)," State Highway Patrol Captain Ron Johnson told a news conference.
“Our officers came under heavy gunfire,” in one area, he said, and riot police had confiscated two guns from protesters and what looked like a petrol bomb (molotov cocktail).
Demonstrations, mostly peaceful but with spasms of violence by smaller groups, have flared since Michael Brown, 18, was shot dead during an incident with a policeman in a patrol car while walking down a residential street in Ferguson on Aug. 9.
An overnight curfew has been imposed and the National Guard, the U.S. state militia, has been deployed in the St. Louis suburb of 21,000 people to stop looting and burning that have punctuated the protests and stirred questions about U.S. race relations.
Missouri state police with an African-American in charge, Johnson, have taken over security efforts from mostly white local police, widely accused of using excessive force against blacks, and President Barack Obama and civil rights leaders have appealed for calm while a federal investigation proceeds.
Brown was shot by policeman Darren Wilson, 28, who is now on paid leave, in hiding and under criminal investigation.
The clashes between riot police and protesters on Monday night occurred after hours of demonstrations that were mostly peaceful, Reuters witnesses said.
Police had closed a roadway to traffic to provide a path for marches but said a smaller group within the larger crowd hurled bottles, rocks and petrol bombs at officers standing near armored vehicles. Police responded by firing gas-filled canisters and a noise cannon to try to disperse the throng.
Johnson, commanding state police now overseeing efforts to reinstate order, told CNN that two people were shot within the crowd, but not by police, and were taken to hospital.
Some demonstrators, including a church minister using a blow horn, urged crowds to calm down.
Local broadcast media said on Twitter that one person was shot in the hand and taken to an area hospital and that another man rushed to a police line holding his side saying he had been shot. Reuters could not confirm the reports.
"This has to stop. I don't want anybody to get hurt. We have to find a way to stop this," Johnson said.
There have been peaceful protests over Brown's killing elsewhere in the United States including in St. Louis, New York, Seattle and Oakland. Johnson said some of the arrested protesters had come from California and New York.
Missouri Governor Jay Nixon declared a state of emergency in Ferguson on Saturday and a curfew from midnight to 5 a.m. He also mobilized the National Guard to back up state police.
Obama said he told the governor the use of the National Guard should be limited and called for conciliation in communities hit by the unrest. U.S. Attorney General Eric Holder will visit Ferguson on Wednesday, Obama said.
"While I understand the passions and the anger that arise over the death of Michael Brown, giving in to that anger by looting or carrying guns, and even attacking the police, only serves to raise tensions and stir chaos," Obama told a news conference. "It undermines, rather than advancing, justice."
Holder said over 40 FBI agents were canvassing Ferguson neighborhoods in their investigation and an additional medical examination was being performed on Brown. Results of autopsies done by federal and St. Louis Countyauthorities were pending.
An autopsy conducted on behalf of Brown's family showed he was shot at least six times, including twice in the head. The path of one bullet indicates Brown may have been lowering his head in surrender when the fatal shot struck, according to Brown family attorney Daryl Parks.
"His head was in a downward position," Parks told reporters. "Given those kind of facts, this officer should have been arrested," Parks said. There were no signs of struggle with the officer and no gunshot residue on the body.
Ferguson police quoted Wilson, the 28-year-old officer who shot Brown, as saying he had asked Brown and a friend to move off the street where they were walking onto the sidewalk. Wilson reported that Brown reached into his patrol car and struggled for his gun when the officer fired the initial shot.
St. Louis County prosecutors' spokesman Edward Magee said the case could be presented this week to an investigating grand jury which would decide whether Wilson will be indicted.
Ferguson has seen a stark demographic shift in recent decades, going from all white to mostly black. About two-thirds of the town's 21,000 population are black, while out of a police force of 53, three officers are black.
Many Ferguson residents say Brown's killing was emblematic of police excesses against blacks, a charge authorities deny.
Brown's friend Dorian Johnson, 22, said Wilson had reached out his car window to grab Brown and the teenager tried to get away. Johnson said Brown held up his hands to surrender but Wilson got out of his car and shot him several times.
The National Bar Association, containing the largest network of black attorneys and judges, filed a lawsuit on Monday against Ferguson and its police department, demanding it protect evidence of the shooting and arrests made during protests.
Looting has left a number of Ferguson stores in shambles.
In July 2013, there were angry albeit peaceful protests in cities across the United States over the acquittal in aFlorida second-degree murder and manslaughter trial of neighborhood watch volunteer George Zimmerman, a white Hispanic, who shot dead an unarmed black teenager, Trayvon Martin, in the street during a scuffle in February 2012.