PRESIDENT Barack Obama has called the police shooting death of an unarmed black teenager a tragedy and urged a thoughtful response after two nights of violent protests, looting and arrests in a St Louis suburb.

But early yesterday, a police officer shot and critically wounded a man who drew a handgun near the site of the protests.

St Louis County Police Department officers responded to reports of four or five men with shotguns and wearing ski masks.

Loading article content

One of them pulled a gun on an officer, who fired at him, police said.

Earlier, police had again fired tear gas into protesters who had confronted a line of officers after a far larger crowd dispersed.

President Obama promised a full investigation by the US Department of Justice into the teenager's death, which has provoked outrage in the largely African-American town of Ferguson.

He said: "I know the events of the past few days have prompted strong passions, but I urge everyone in Ferguson, Missouri, and across the country, to remember this young man through reflection and understanding."

Friends and family of 18-year-old Michael Brown held a peaceful church vigil on Tuesday night after his father pleaded for an end to the violence.

Standing with supporters, including the Reverend Al Sharpton, Michael Brown Sr. said he wanted justice but wanted it "the right way."

Several hundred protesters appeared to heed the calls for non-violence, chanting "hands up, don't shoot" and "no justice, no peace" during a tense but ultimately peaceful stand-off with police clad in riot gear and flanked by armored vehicles near the site of Mr Brown's death.

Missouri Governor Jay Nixon told a packed church the community was "reeling from what feels like an old wound that has been torn open afresh."

In a separate incident simmering in California, a vigil was also planned following Monday's shooting death of an unarmed 24-year-old black man in Los Angeles.