Police shot and killed another 18-year-old black boy on Wednesday 10 days after the first anniversary of death of Michael Brown in north St. Louis, Missouri.

The police officers in St. Louis, which hit the headlines for its suburb Ferguson where Brown was killed, said the young man they fatally shot had pointed a gun at them.

They later identified the victim as Mansur Ball-Bey, aged 18.

Some 200 demonstrators gathered at the scene after the shooting. Chanting "Black Lives Matter," they questioned the police use of deadly force.

St. Louis County Police Chief Sam Dotson told reporters at a press conference that two young armed male suspects ran out of the back of a house, and two police officers chased the suspects.

During the chase, one of the suspects raised his gun and pointed it at officers, the officers then shot at the suspects, killing one, while the other got away. The two officers are not injured and are on administrative leave now.

Tensions remain high in St. Louis area after unrest during the anniversary of Brown's death. Unarmed Brown was fatally shot by a white police officer on August 9, 2014. A St. Louis County grand jury and the U.S. Justice Department declined to charge the officer.