A second woman has accused Senator Al Franken of touching her inappropriately – this time, while he was a sitting senator.

Lindsay Menz, a 33-year-old resident of Frisco, Texas, told CNN that Mr Franken grabbed her rear end while posing for a photo at the Minnesota State Fair in 2010. The allegation comes days after radio news anchor Leeann Tweeden accused the Senator of kissing her and groping her without her consent in 2006, when he was working as a comedian.

Mr Franken has apologised to Ms Tweeden for the incident. He told CNN he did not remember taking the photo with Ms Menz, but said he felt “badly that Ms Menz came away from our interaction feeling disrespected”.

Ms Menz said the incident occurred in the summer of 2010, nearly two years after Mr Franken was elected senator. She was spending the day at a local radio booth sponsored by her father and taking pictures with public figures who stopped by.

Ms Menz said she and her husband recognised Mr Franken right away. After a cordial exchange, Ms Menz’s husband moved to take a picture of his wife with the Senator. That’s when Ms Menz said Mr Franken pulled her in close – “like awkward close” – and put his hand on her rear.

"It wasn't around my waist. It wasn't around my hip or side. It was definitely on my butt," she told CNN. "I was like, oh my God, what's happening."

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Ms Menz said she confided in her husband afterward that the Senator “totally grabbed my butt”. Mr Menz confirmed this. Ms Menz's mother, Jodi Brown, also said she remembered talking with her daughter about the incident after it happened.

Ms Menz posted the photo to Facebook at the time. In comments visible to Ms Menz’s Facebook friends, her sister wrote: "Sorry, but you two aren't Bibles (sic) width apart" – a reference to how close the two are in the photo.

"Dude – Al Franken TOTALLY molested me! Creeper!" Ms Menz responded.

In a statement, Mr Franken said: "I take thousands of photos at the state fair surrounded by hundreds of people, and I certainly don't remember taking this picture. I feel badly that Ms. Menz came away from our interaction feeling disrespected."

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Mr Franken is already facing a Senate ethics investigation for the allegations made by Ms Tweeden. The radio host claimed last week that Mr Franken had kissed her without her consent while the two were rehearsing a skit for their USO Tour of the Middle East. She also claimed he had touched her breasts while she was sleeping on the flight home, and provided a picture of that appears to show Mr Franken reaching for her chest while she sleeps.

Mr Franken said he remembered the kiss differently, but apologised to Ms Tweeden and said he would fully cooperate with an ethics investigation into the incident.

Mr Franken is not the only politician to have been accused of inappropriate touching during a photo op. Six women have accused former President George HW Bush of grabbing their buttocks while posing for photos – including one woman who says she was only 16 at the time.