US authorities are investigating after a disturbing video of a woman beating a dog went viral on Twitter, prompting a wave of outrage.

The video, believed to have been filmed in Boise, Idaho, shows a woman wearing boxing gloves punching a german shepherd hard in the face.

As a man films, the woman hits the dog multiple times over the 13-second clip as the man says: "We're boxing animals".

"I hit him so hard," the woman says as the video cuts off.

The woman was quickly identified online and set her accounts to private after facing a huge backlash.

A social media user claiming to have been in conversation with the woman in the video published a screenshot of a conversation where the woman defends her actions.