Leeann Tweeden posted the allegations on the website of KABC, a Los Angeles radio station where she now works as a news anchor for a morning radio show. Tweeden joined the then-comedian on one of several trips to entertain troops in December 2006 when Franken told her he wrote a skit for the pair that included a kiss. And despite her protests, she alleges he insisted they practice the kiss during rehearsal.
"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 wrote.
Tweeden also included a photo of her sleeping on board an aircraft later during the trip, in which Franken is shown reaching out as if to grope her breasts.
Franken said in a statement that Tweeden's account of the skit did not match his memory.
"But I send my sincerest apologies to Leeann," Franken wrote. "As to the photo, it was clearly intended to be funny but wasn't. I shouldn't have done it."
Speaking on her radio show Thursday morning, Tweeden said she didn't come forward with the allegations sooner because she feared her career, including a stint as a swimsuit model, would lead others to discount her story.
"I felt belittled. I was ashamed. I've had to live with this for 11 years," she said on-air. "Somehow it was going to be my fault. It was not going to be worth the fight."
Franken is a longtime comedian and "Saturday Night Live" writer who won a Minnesota seat in the U.S. Senate after a lengthy recount in 2009.
He drew criticism during his first Senate campaign for joking about rape while discussing a sketch idea during his days on NBC's "Saturday Night Live." Franken said then that he regretted some of the things he had written, and said he respected women "in both my personal and professional life."
Franken becomes the latest figure swept up in sexual harassment allegations that have mushroomed since Hollywood figure Harvey Weinstein was hit with multiple allegations. Concerns about sexual harassment are widespread in Congress, where House Speaker Paul Ryan has ordered mandatory training.
Tweeden said the surge of people coming forward with their own experiences of sexual harassment or assault encouraged her to go public with her account about Franken.