Democratic Senator Al Franken has been accused of sexual assault as the national discussion about sexual harassment moves to the US capitol.

Leeann Tweeden, a morning news anchor for a Los Angeles radio station, claimed in an article for 790 KABC that Mr Franken kissed her and groped her without her consent during a tour through the Middle East. The Senator has apologised, and asked for an ethics investigation into his own conduct.

In 2006, Ms Tweeden and Mr Franken – who worked as a comedian at the time – embarked with several other performers on a United Service Organizations (USO) Tour to entertain American troops. Ms Tweeden said she only expected to host the show they performed, but that Mr Franken wrote her into one of the skits. The skit, she said, included a kiss between their two characters.

On the day of the show, Ms Tweeden alleged, Mr Franken pressured her to rehearse the kiss, despite her protestations. When she finally relented, she said, he “put his hand on the back of my head, mashed his lips against mine and aggressively stuck his tongue in my mouth”.

Ms Tweeden said she pushed him away, and warned him not to do it again.

In an initial statement, Mr Franken said: “I certainly don’t remember the rehearsal for the skit in the same way, but I send my sincerest apologies to Leeann.”

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Mr Franken later expanded on his statement, extending his apology to "everyone else who was a part of that tour, to everyone who has worked for me, to everyone I represent, and to everyone who counts on me to be an ally and supporter and champion of women".

"I respect women," he continued. "I don't respect men who don't. And the fact that my own actions have given people a good reason to doubt that makes me feel ashamed."

The news anchor’s story did not stop there, however. Ms Tweeden said she avoided Mr Franken throughout the tour, and made sure she was never left alone with him – actions she said he retaliated against with “petty insults”.

Leeann Tweeden is given an MP armband as she arrives at Baghdad International Airport on 19 June, 2003 (TIMOTHY A. CLARY/AFP/Getty Images)

It wasn’t until after the tour ended, however, that Ms Tweeden said she stumbled upon an upsetting photograph. The photo – which Ms Tweeden has made public – appears to show Mr Franken groping her breasts over her military gear while she sleeps.

“I couldn’t believe it,” Ms Tweeden said of her reaction to the photo. “He groped me, without my consent, while I was asleep. I felt violated all over again. Embarrassed. Belittled. Humiliated.”

She added: “How dare anyone grab my breasts like this and think it’s funny?”

In his second statement, Mr Franken said there was "no excuse" for his actions in the photo.

"I look at [the photo] now and I feel disgusted with myself," he said. "It isn't funny. It's completely inappropriate. It's obvious how Leeann would feel violated by that picture."

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Several Democratic senators condemned the alleged behaviour, with Senator Claire McCaskill calling it "completely unacceptable". Senator Kirsten Gillibrand called the allegations "disturbing".

Republican Senate Majority Leader Mitch McConnell called on the Congressional Ethics Committee to review the allegations – a suggestion Mr Franken welcomed in his statement.

"I am asking that an ethics investigation be undertaken, and I will gladly cooperate," the Senator said.

Ms Tweeden said she was inspired to share her story after interviewing Representative Jackie Speier, who has solicited stories of sexual harassment from women working in the Capitol – and also shared her own.

At a Congressional hearing this week, Ms Speier said women had told her of legislators exposing their genitals to co-workers and grabbing their victims’ private parts on the House floor. She added that she knew of two current Congress members – one Democrat and one Republican – who had sexually harassed staffers.

Ms Tweeden said she wanted to have the same effect on victims of sexual harassment that Ms Speier had on her.

“I want them, and all the other victims of sexual assault, to be able to speak out immediately, and not keep their stories – and their anger – locked up inside for years, or decades,” she said.