A 28-year-old woman was indecently assaulted after a man started chatting to her on a Burnley street.
The incident, at 3.30am on Sunday, happened after the woman walked from Church Street to Lindsay Street.
Det Sgt Steve Mounsey said: "She was approached by the man on Church Street and he engaged her in conversation.
"He followed her to Lindsay Street then took hold of her from behind and turned her round and she saw he was indecently exposing himself. She knocked on a door and he ran off."
Police are appealing for anyone who might have seen the man running off to get in touch.
The man was wearing a white, short sleeved T-shirt with a Union Jack motif across the front from shoulders to waist which looked like it was brush painted.
He is white, 5ft 9ins, slim, in his early 20s with blond to brown hair shaved to a 'number one' cut.
Anyone with information should contact Burnley CID on 01282 425001.
Police said there was no link to previous indecent assaults in the Burnley area in recent weeks.
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