Washington, Nov 17
US Senator Al Franken has responded to a woman's allegations that he groped her as she slept and "forcibly" kissed her in a rehearsal for a comedy skit.

Leeann Tweeden -- a radio host and former model -- said the two incidents happened in December 2006 on a tour to entertain US troops overseas, before Franken entered politics, BBC reported.

Franken, the US Senator from Minnesota, responded immediately to the accusation on Thursday in a written statement, saying he was sorry for his actions during a 2006 United Service Organizations (USO) tour and calling for a Senate ethics investigation into his behaviour, Efe news reported.

Tweeden, 44, used a blog post to level the accusations against Franken, who was a well-known comedian -- but not yet a senator - when the two were part of a tour to entertain US troops in the Middle East.

"You knew exactly what you were doing," Tweeden wrote on the Web site of her employer, Los Angeles radio station KABC.

"You forcibly kissed me without my consent, grabbed my breasts while I was sleeping and had someone take a photo of you doing it, knowing I would see it later and be ashamed."

Tweeden, who did not call on Franken to resign and did not weigh in on whether the Senate should investigate him, said there might be another female victim.

"I've gotten a phone call from a woman... I've only gotten a message... that says something similar has happened to her. And I haven't returned it yet. So that's to be determined. I don't know," Tweeden said in a subsequent press conference.

During the tour, Franken wrote a sketch in which his character and Tweeden's were to kiss and insisted upon rehearsing the scene.

"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 wrote.

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

In a separate incident during the entertainers' flight back to the US on a military transport plane, Franken posed for a photo in which he appears to grope Tweeden's breasts while she is sleeping.

The 66-year-old Franken, who was first elected to the Senate in 2008 and re-elected in 2014 for a second six-year term, apologised for his actions in a statement.

"The first thing I want to do is apologize: to Leeann, to everyone else who was part of that tour, to everyone who has worked for me, to everyone I represent," he wrote.

While he said there was no excuse for the photo, he said he had a different recollection concerning the rehearsal of the sketch.

"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," Franken wrote.

"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."

The accusation against Franken comes amid a slew of sexual allegations against powerful men, including prominent Hollywood figures and the Republican candidate in an upcoming Senate election in Alabama, Roy Moore.

US senator apologises for grope caught on camera