Obama 'deeply disturbed' by Chicago police shooting

President Barack Obama said Wednesday he was "deeply disturbed" by video of a white Chicago policeman shooting dead a black teenager, in the latest such incident to roil the United States.

Graphic footage released shortly after officer Jason Van Dyke was charged with first-degree murder on Tuesday has reignited impassioned debate about the use of force by law enforcement in the US, with Chicago left dangerously on edge.

Protesters there have likened the Laquan McDonald killing to that of Michael Brown, the black teenager shot dead by a white policeman in Ferguson, Missouri last year, triggering 15 months of demonstrations in major US cities over perceived police brutality against black men.

A small band of demonstrators hit the chilly Chicago streets for a second night in a row Wednesday, reportedly confronting police officers.

Chicago police initially said that McDonald was high on the hallucinogen PCP, acting erratically and then lunged at officers with a knife when he was shot 16 times in October 2014.

But police dashcam video showed the 17-year-old walking away when Van Dyke opened fire and made no threatening gestures to justify the use of deadly force, prosecutors say.

"Like many Americans, I was deeply disturbed by the footage of the fatal shooting of 17-year-old Laquan McDonald," Obama wrote on his official Facebook page.