Image copyright Facebook/ Detroit Police Image caption Detroit Police Chief James Craig said he was "angry" about the officer's actions

A Detroit policeman has been demoted after posting a "racially insensitive" Snapchat video of him mocking a black woman he pulled over in a traffic stop.

Officer Gary Steele stopped Ariel Moore, 23, on Tuesday after finding her car's number plate had expired.

He then filmed her walking home in the dark and used a "black history month" filter displaying the caption: "what black girl magic looks like".

An investigation has been launched, and the officer has been reassigned.

In a news conference on Thursday, Detroit Police Chief James Craig condemned the video as "derogatory" and "racially insensitive".

"I'm not troubled, I'm not disappointed. I am angry," he said of the policeman's "bad decision" to upload a "problematic" Snapchat video of the encounter.

According to police, Ms Moore was stopped by Officer Steele and another unidentified officer who called to have her car impounded after finding her license plate was expired and she had no vehicle insurance.

Bodycam video shows that she was offered a ride home by the officers, but refused since she was only one block away.

In the Snapchat video, with the filter "celebrate black history month" appearing on-screen, the officer is also heard commenting "walk of shame in the cold".

He is also heard on-camera saying "bye Felicia" as she walked through snow-covered streets.

Black history month began on 1 February, and is commemorated all month in the US.

Temperatures in Detroit have been far below freezing, as a "polar vortex" has put much of the northern US under a deep freeze.

An investigation in the officer's action has begun, and the chief added that the department is taking steps to strip him of his corporal's rank.

"He has a troubling history," he added, in a reference to Mr Steele's 2008 arrest for a domestic attack on his girlfriend, in which he fired a gun near her head.

The 18-year-police veteran pleaded guilty, served probation and was allowed to remain on the force, according to Detroit media.

Last September a white Detroit police officer was fired after posting a Snapchat photo of himself in uniform with the caption "another night to Rangel (sic) up these zoo animals".