A white police officer who in August fatally shot unarmed black teenager Michael Brown in Ferguson, Missouri, resigned from the police force, his lawyer announced Saturday.

Darren Wilson, 28, resigned from the Ferguson Police Department after it had received threats of violence if he remained an employee, according to a report by local St. Louis Post-Dispatch newspaper.

Last week a Missouri grand jury, after three months of investigation, decided to not indict Wilson for shooting dead 18-year-old Brown, triggering riots gripping the St. Louis suburb and the nation.

One of his lawyers, Neil Bruntrager, told U.S. media the resignation was effective immediately.

The Aug. 9 shooting of Michael Brown has inflamed a debate over the issue of race relations and police brutality in the country.

Wilson, whose resignation was expected, has been on a paid administrative leave since the incident.

Protests in Ferguson continued Saturday, with nearly 150 demonstrators gathering outside the police station.

The protesters, who staged a sit-in on a street near the station, burned an American flag during the demonstration, Anadolu Agency journalists at the scene reported.

Police arrested several protesters who refused to clear the street, which was briefly blocked.

•Photo shows killer policeman Darren Wilson.