A Milwaukee police officer was being targeted by online threats Tuesday from people who say he fatally shot the black man whose death has sparked violence in the city.

Police haven't released the name of the officer who shot Sylville Smith on Saturday, but widely shared social media posts and at least one news report identified him as a 24-year-old patrolman. Many posts contained threats against him and a photo.

The department said in a statement Tuesday it has noticed a "disturbing national trend" in which social media users have identified officers involved in fatal shootings and threatened them and their families. A spokesman declined to confirm the identity being circulated online.

The department is aware of some local threats against its officers and is investigating, according to the statement.

Smith, 23, was shot and killed Saturday after a brief foot chase that followed a traffic stop. Police say Smith had a gun in his hand when he turned toward the officer, who opened fire. The state is investigating.

The officer, who has not been identified, is black, as was Smith.

A few hours after the shooting, violence erupted on the city's largely black north side, with protesters hurling rocks at police and burning six businesses. A lighter night of protests followed Sunday. Monday was calm, though 10 people were arrested.