Michael Brown shooting: Second Missouri police killing
The police killing of a second black man in Missouri in 11 days has threatened to further escalate tension.
On Tuesday, police officers shot dead a man who brandished a knife at them, St Louis Police Chief Sam Dotson said.
The 9 August shooting of Michael Brown, 18, sparked days of violent protests in the town of Ferguson, prompting a heavy police crackdown.
There is widespread anger against the mainly white police force for killing Mr Brown, who was unarmed.
Mr Brown's family say his funeral will take place on Monday.
US Attorney General Eric Holder is due to visit Ferguson on Wednesday to meet officials investigating the killing.
Tuesday's police shooting has threatened to further inflame tensions within the community.
According to police, in the early afternoon, two officers shot and killed a knife-wielding man four miles (6.4km) from the site of Mr Brown's killing.
St Louis Police Chief Sam Dotson said witnesses reported the man had been behaving in an erratic manner, and emphasised the officers had a right to defend themselves.
"The suspect turned toward officers, pulled out knife in an overhand grip, told officers to 'shoot me now, kill me now'," he told reporters.
In another development in the Michael Brown case, the St Louis county prosecutor's office on Tuesday said it would present evidence against the officer who killed Mr Brown to a grand jury on Wednesday.
The citizen panel will determine whether or not to charge Darren Wilson with a crime.
Both St Louis officials and the US justice department are conducting investigations into the case, which has provoked demonstrations throughout the country.
Witnesses have said Mr Brown was shot as he held his hands up in a position of surrender, while the police and supporters of Mr Wilson have said he fired during a fight with Mr Brown.
An autopsy commissioned by Mr Brown's family concluded he had been shot six times, twice in the head.
New York pathologist Dr Baden said his body showed no signs of a struggle.
He also believed Mr Brown was not shot at close range as there was no gunpowder residue on his body, suggesting the officer was more than 2ft (60cm) away.
On Monday night protests in Ferguson again turned violent, despite the presence of troops from the National Guard.
Missouri Highway Patrol Capt Ron Johnson, who has led the police response since Thursday, said officers were forced to use tear gas and stun grenades after they came under "heavy gunfire" and were attacked with petrol bombs and bottles.
He said two people were hit by gunfire from demonstrators, insisting that officers did not use their weapons.
Capt Johnson appealed to demonstrators to protest in the daytime to prevent a "tiny minority of law breakers" from deliberately sparking violence.
"Anyone who has been at these protests understands that there is a dangerous dynamic in the night: it allows a small number of violent agitators to hide in the crowd and then attempt to create chaos," he told journalists.
Those arrested include people from other states, including New York and California, Capt Johnson said. Correspondents say this suggests the protests are becoming more organised.
Separately, President Barack Obama said he understood the "passions and anger" provoked by the death of the teenager.
"In too many communities, too many young men of colour are left behind and seen only as objects of fear," he said.
Population of Ferguson, Missouri
Black or black African
6% Police officers are black
21% Families living below the poverty line