A woman who made a Nazi salute outside of Donald Trump's cancelled rally in Chicago has tried to explain her gesture after being confused with a Bernie Sanders worker.

Birgitt Peterson, 69, of Yorkville, Illinois, appears in a photo published by the Chicago Tribune, wearing a Trump t-shirt, a cigarette in her left hand.

Her right arm is raised into the air, fingers outstretched and palm facing down, reproducing the Nazi salute adopted by Adolf Hitler's supporters in the 1930s.

Peterson, who was born in West Berlin in 1946, a year after Hitler's death, told The New York Times she made the gesture in response to anti-Trump protesters who were comparing The Donald to the German dictator.

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Birgitt Peterson (pictured), 69, of Yorkville, Illinois, made a Nazi salute after Donald Trump's cancelled rally in Chicago on Friday. Peterson, who was born in West Berlin in 1946 and later became a US citizen, said she made the gesture in response to anti-Trump protesters who were comparing The Donald to Adolf Hitler

Donald Trump Jr retweeted a message wrongly identifying the woman in the photo as Sanders supporter Portia Boulger

'They said Trump is a second Hitler,' Peterson said. 'I said: "Do you know what that sign stands for? Do you know who Hitler really was?"

'I make the point that they are demonstrating something they had no knowledge about, If you want to do it right, you do it right. You don't know what you are doing.'

Peterson, who became an American citizen in 1982, told The New York Times she was 'absolutely not' a Nazi and found it insulting when people accused her of being one based on the photo.

Some previously claimed the woman in the photo wasn't Peterson but Portia Boulger, 63, a Bernie Sanders supporter from Chillicothe, Ohio.

Among them was Donald Trump Jr, who retweeted a message wrongly identifying the woman as Boulger.

'Big surprise. However, the media will never run this,' Trump's son wrote in his own tweet.

He has since deleted his message without apologizing or acknowledging his mistake.

Boulger, a former union carpenter who now works part-time as a teacher, told The Daily Beast she was making phone calls on behalf of Sanders during Trump's cancelled rally in Chicago on Friday.

She said she could see a little bit of resemblance between herself and Peterson when her own hair was longer, but it's shorter now.

Some Twitter users are now asking Trump Jr to give Boulger an apology and are using the hashthag #ApologizeTrumpJr.