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The violence has captured headlines around the world, raising questions about the state of US race relations nearly six years after Americans elected their first black president.
Law enforcement has made various efforts to soothe angry demonstrators, but police said they had come under heavy gunfire overnight and arrested 31 people despite the deployment of Missouri National Guard troops and the lifting of a curfew to allow protesters to have more freedom to demonstrate.
"We overpoliced for a few days, and then we completely underpoliced," US Senator Claire McCaskill, a Missouri Democrat who was traveling to Ferguson on Tuesday (local time), told cable channel MSNBC.
She said she was working with local leaders on ways to quell the violence. Possible methods include screening for weapons and moving protest areas away from the business district to open green spaces.
Both she and US Representative Emanuel Cleaver, another Missouri Democrat, said calm was needed to allow federal investigators to evaluate the evidence.
"What's happening now is damaging, or interfering, with what needs to be done," Cleaver told MSNBC.
On Monday, President Barack Obama said he told Missouri Governor Jay Nixon that use of the National Guard should be limited, and he also called for conciliation. Attorney General Eric Holder plans to visit Ferguson on Wednesday.
Ferguson, a community of roughly 21,000 mostly black residents just outside St. Louis, has a long history of racial tension. Blacks have complained of police harassment and under-representation in city leadership.
Tension boiled over 10 days ago after 18-year-old Michael Brown was shot dead while walking with a friend down a residential street on the afternoon of August. 9.
The police refused to immediately release the name of the officer who killed Brown. They later identified him as 28-year-old Darren Wilson but and still have not provided details about why he fired multiple rounds at Brown.
Both the US Department of Justice and the St. Louis County Police Department are investigating the shooting. The county prosecutor's office said it could start presenting evidence to a grand jury on Wednesday to determine if Wilson will be indicted.
Since the killing, thousands of protesters have taken over the site of the shooting and the nearby business district each night, chanting anti-police slogans and carrying signs calling for Wilson's arrest.
Some journalists covering the confrontations have been hit by tear gas and arrested.
On Tuesday, the Vienna-based Organization for Security and Co-operation in Europe, an intergovernmental security and human rights organisation whose members include 57 countries including the United States and Canada, criticized the treatment of the journalists.
On Monday night, officials had hoped that the lifting of a curfew imposed over the weekend would cool tensions and end the looting and violence. Police also closed a roadway to traffic to provide a path for marchers.
But police said some in the crowd hurled bottles, rocks and petrol bombs at officers, who responded by firing gas-filled canisters and a noise cannon to try to disperse the throng.
State Highway Patrol Captain Ron Johnson, who is overseeing security in Ferguson, said officers had come under "heavy gunfire" but did not return it. Riot police did confiscate two guns and what looked like a petrol bomb from protesters.
Four officers were injured, he said.
Johnson separately told CNN that two people were shot within the crowd, but not by police, and were taken to hospital. There was no immediate word on their condition.
"This has to stop," said Johnson, an African-American who grew up in the area. "I don't want anybody to get hurt. We have to find a way to stop this."
The disturbances are the worst since the angry but peaceful protests across the United States in July 2013, over the acquittal of George Zimmerman, a white Hispanic who killed unarmed black teenager Trayvon Martin during a scuffle in Florida.