A man is assisting police after CCTV of a brutal 'coward punch' attack outside a pub in south Canberra was released online.

In the security vision, a shirtless man with green pants can be seen approaching a man in a dark shirt, asking the man for a lighter.

He suddenly delivers a brutal unprovoked blow to the man's face before shoving him against the outside of PJ O'Reilly's pub in Tuggeranong suburb Greenway.

View photos Photo: Facebook/ACT Police More

View photos Photo: Facebook/ACT Police More

The shirtless man pauses for a moment before apparently launching himself at the victim a second time, appearing to grab him around the neck.

A woman in a black dress quickly moves in to help, trying to wrestle the shirtless man's grip from the victim.

View photos Photo: Facebook/ACT Police More

View photos Photo: Facebook/ACT Police More

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