Democrat presidential candidate Hillary Clinton has hit out at Donald Trump and the GOP, suggesting they are sexist.

Clinton's comments came days after Trump said the first female presidential candidate "did not have a presidential look" and after Republican National Committee Chairman Reince Priebus said she didn't smile at the recent Commander-in-Chief Forum.

Responding to a press question about whether she believed she experienced different treatment as a female candidate, Clinton said in comments carried by CNN: "I'm going to let all of you ponder that last question.

"I think there will be a lot of PhD theses and popular journalism writing on that subject for years to come. I don't take my advice and I don't take anything seriously that comes from the RNC."

Clinton has been asked the question after Priebus wrote on Twitter: "Hillary Clinton was angry and defensive the entire time – no smile and uncomfortable – upset that she was caught wrongly sending our secrets."

Clinton also responded on Twitter, sharing footage of her press conference after the Commander-in-Chief Forum, and making a dig at Trump and the RNC, stating: "Last night Trump chose to talk about his deep admiration and support for Putin. Maybe he did it with a smile and I guess the RNC would have liked that."

Sexism has previously been a topic of discussion on the campaign trail after Trump accused Clinton of playing the "woman card" during the primary season in April, stating: "I think the only card she (Clinton) has is the women's card. She has nothing else going.

"And, frankly, if Hillary Clinton were a man, I don't think she'd get 5% of the vote. The only thing she has going is the woman's card. And the beautiful thing is women don't like her, ok? And look how well I did with women tonight. So, ladies and gentlemen, thank you very much."

However, Clinton turned the "woman card" into a campaign tool, hitting back at Trump, saying: "If fighting for women's healthcare and paid family leave and equal pay is playing the woman card, then deal me in." "Deal Me In" has since been used as one of Clinton's slogans.