Police investigating the deliberately-lit fire that has torn through more than 3200 hectares of bushland on the south-western outskirts of Sydney want to speak with a group of men seen in a video on social media.

Around 9.30am on Tuesday, Bankstown police received the video footage after it was posted to Snapchat, showing a group of men cavorting around a grassfire as flames began to engulf nearby trees.

Images of the three men police wish to speak to. Credit:Seven News

It's believed the video, which shows the men laughing and cracking jokes as the small fire around them grows, may have been shot in Heathcote – one of the areas the weekend bushfire burnt through.