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Two people were shot and dozens arrested overnight in the Missouri town of Ferguson as racially charged unrest continued to roil its streets more than a week after a killing of an unarmed black teen by a white policeman.
Police said a small minority of protesters within a larger demonstration fired guns and tossed rocks and Molotov cocktails at officers, who responded with tear gas.
Two people in the crowd were wounded by the protesters' gunfire and 31 were arrested, said Captain Ron Johnson of the Missouri Highway Patrol, adding that the police did not open fire.
He said four officers were also injured in the fresh bout of violence that has shaken the Saint Louis suburb and gripped the United States in a new debate over police treatment of minorities.
On August 9, 18-year-old Michael Brown was shot dead in broad daylight on a residential street by a Darren Wilson, a 28-year-old white police officer.
Yesterday's demonstration over the killing started peacefully, only hours after President Barack Obama made a national televised appeal for calm.
But Johnson said a group of about 200 then started moving toward the police and a small minority among them attacked.
"There is a dangerous dynamic in the night," Johnson said. "It allows a small number of violent agitators to hide in the crowd and then attempt to create chaos."
He added: "Our officers came under heavy gunfire."
Johnson stood behind a table on which a gun and a Molotov cocktail he said had been seized from protesters were on display.
Some of those in the crowd were not locals but rather had come from as far away as New York and California, he said.
US National Guard troops rolled into Ferguson earlier in the day, but they kept a low profile as police in riot gear dispersed the demonstrators around 11 pm (0400 GMT).
Obama, the nation's first African-American president, said he was sending Attorney General Eric Holder to Ferguson on Wednesday as Washington pursues a civil rights investigation into the case.
Obama said there was no excuse for local police to employ "excessive force" and urged the state of Missouri to make only "limited" use of the National Guard, which is operating under the supervision of Johnson and the Missouri Highway Patrol.
The reinforcements allowed State Governor Jay Nixon to lift an overnight curfew, but tempers are still running high amid controversy over Brown's death.
