An off-duty St Louis city policeman shot and killed a suspect who fired on him, police officials have said.
The shooting led to protests just miles from the suburb of Ferguson, which was the scene of another controversial police shooting in August.
The 32-year-old officer, who was working for a security company but wearing his police uniform, attempted to stop a suspect who then fled, St Louis Police Department spokeswoman Schron Jackson said.
The suspect, whom police described as a black man between 18 and 20 years old, turned and fired at the pursuing officer, who returned fire and fatally wounded him, Ms Jackson said.
Police did not provide his name.
The officer, who is a six-year veteran of the department and is white, was not hurt and a gun was recovered from the scene, Ms Jackson said.
The officer has been placed on administrative leave according to the department's policy, Ms Jackson said, and the investigation continues.
Suspect turned & fired at officer. Fearing for his safety, officer returned fire striking the suspect, fatally wounding him.
— St. Louis, MO Police (@SLMPD) October 9, 2014
A large crowd of protesters assembled at the scene in south St Louis, near the city of Ferguson, which has seen near nightly protests following the fatal 9 August shooting of 18-year-old Michael Brown by white police officer Darren Wilson.
Around 200 demonstrators chanted in the streets, with dozens shouting directly at police officers.
At one point, a dozen people punched and kicked two occupied police vehicles, one that was marked and another that was unmarked.
Teyonna Myers told the St Louis Post-Dispatch newspaper that she was the cousin of the suspect and that he was unarmed when he was killed.
"He had a sandwich in his hand, and they thought it was a gun. It's like Michael Brown all over again," she told the paper.
The shooting occurred in the neighbourhood of Shaw, a historic district with low levels of crime.
As of September, there had been no homicides and five cases of aggravated assault, according to police crime statistics.
