Police in the US are investigating a detective who appears to draw his gun during a mass snowball fight on the streets of Washington DC.

The video appears to show the detective holding a gun in his left hand as he begins to approach a large group of people, which had gathered for the snowball fight.

People in the crowd can be heard saying "he has a gun".

Police say they are looking into reports that the plain-clothed police officer stepped out of his own vehicle and drew his weapon after his car had been hit by snowballs.

The video was provided by Reason.TV, a libertarian organisation in the United States.