US senator Al Franken accused of sexual assault

Former comedian and current US senator Al Franken has apologised after a photo was released showing him seemingly groping a sleeping woman.

Mr Franken has been accused of kissing and assaulting Los Angeles-based news presenter Leeann Tweeden during an entertainment tour in 2006.

The Democratic senator has issued an apology, saying he's "ashamed" and "respects women".

Ms Tweeden claimed Mr Franken kissed her during a rehearsal for a skit in an opinion piece published by KABC radio on Thursday (local time).

"We did the line leading up to the kiss and then he came at me, put his hand on the back of my head, mashed his lips against mine and aggressively stuck his tongue in my mouth," she said.

"I immediately pushed him away with both of my hands against his chest and told him if he ever did that to me again, I wouldn't be so nice about it the next time.

"I walked away. All I could think about was getting to a bathroom as fast as possible to rinse the taste of him out of my mouth. I felt disgusted and violated."

She also shared a picture which appears to show Mr Franken groping her chest while she was asleep.

"I couldn't believe it. He groped me, without my consent, while I was asleep," she wrote.

"I felt violated all over again. Embarrassed. Belittled. Humiliated.

"How dare anyone grab my breasts like this and think it's funny?"

Mr Franken has responded to the allegations in an apology posted to his Facebook page.

"While I don't remember the rehearsal for the skit as Leeann does, I understand why we need to listen to and believe women's experiences," he wrote.

"I don't know what was in my head when I took that picture, and it doesn't matter. There's no excuse. I look at it now and I feel disgusted with myself. It isn't funny. It's completely inappropriate.

"I respect women. 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."

White House press secretary Sarah Sanders told reporters on Thursday (local time) a formal inquiry into Mr Franken's actions would be an "appropriate action".