BBC – Police and protesters clashed again, 10 days after an officer shot dead an unarmed black teenager
The police killing of a second black man in Missouri in 11 days has threatened to further escalate tension.
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.
