FERGUSON, Mo. - A St. Louis-area police officer was suspended indefinitely on Wednesday for pointing a semi-automatic assault rifle at a peaceful demonstrator as tensions flared during protests over the Aug. 9 police shooting of black teenager Michael Brown.

The incident just before midnight on Tuesday punctuated the 11th straight night of racially charged demonstrations in the St. Louis suburb of Ferguson, Missouri, since Brown, an unarmed 18-year-old, was slain by a white police officer.

No one was hurt in the gun-pointing confrontation, but the incident underscored what many have criticized as heavy-handed and unprofessional police tactics that have helped stoke continuing civil unrest.

(WARNING: Video contains graphic content)

According to an official account from the St. Louis County Police Department, an unnamed policeman from the neighboring community of St. Ann leveled his weapon at a Ferguson protester "after a verbal exchange," and that a superior county officer, a sergeant, quickly intervened.

The sergeant "immediately took action, forcing the officer to lower the weapon and escorting him away from the area," a statement from the county department said.

In video footage of the episode widely circulated on social media, the white officer in question, wide-eyed and agitated, is seen pointing his rifle at numerous demonstrators and members of the media.

At one point, he is heard yelling, "I will f---ing kill you, get back, get back," before the sergeant calmly steps in to defuse the situation, orders him to lower the weapon and leads him away from cameras.

"The unified command strongly feel these actions are inappropriate, and not indicative of the officers who have worked daily to keep the peace," the police statement said.

It said the officer in question had been relieved of duty and suspended indefinitely but gave no further details of any investigation or discipline he might face.

SUCCESS! In response to our letter, officer who threatened to kill #Ferguson protesters has been removed from duty https://t.co/53WP8Ht0Mu — ACLU of Missouri (@aclu_mo) August 20, 2014

In an unrelated videotaped confrontation from earlier in the day in St. Louis that also went viral, police shot and killed a 23-year-old black man who they said brandished a knife at officers and yelled at them to "shoot me now, kill me."

The two officers, who were placed on administrative leave pending an investigation, opened fire after the man refused repeated orders to drop his weapon, police said.

The incident occurred a few miles from the scene of the protests in Ferguson near a convenience store where the man had snatched some drinks and snacks before police were called.

Footage of that incident, in which the man is seen moving toward police with his arms downward after exhorting them to shoot, led some observers to question why officers resorted to deadly force rather than use a Taser stun gun to subdue him.

"There are other ways to stop people if you feel you are in danger than shooting them," said Linda Gladson, 63, a white resident of St. Louis who has spent 20 years as an urban planner in the city.

"We need to stop using lethal force as a first option," she said, standing outside the St. Louis County Justice Center on Wednesday holding a homemade sign that read: "Taser Then Talk!!!"

The fatal shooting sparked concerns about a possible escalation of public anger in the aftermath of the Brown slaying, but as of late on Wednesday had yet to measurably add to the overall level of prevailing tension in the area.