A US army veteran is accusing Senator Al Franken of having touched her breast while posing for a photo on a 2003 tour to entertain troops in Kuwait.
Stephanie Kemplin, a 27-year-old military police officer at the time, says she was left feeling frozen.
She is the fifth woman to have accused Mr Franken of inappropriate touching.
Referring to the latest accusation, Mr Franken’s spokesperson told CNN that he “has never intentionally engaged in this kind of conduct”.
“As Sen Franken made clear this week, he takes thousands of photos and has met tens of thousands of people… He remains fully committed to co-operating with the ethics investigation,” the spokesperson said.
In a press conference on his return to Washington earlier this week, the Minnesota Democrat said he was “ashamed” of his past behaviour.
“I was in a warzone,” she recalled in a tearful interview, questioning whether the former comedian had come to “boost the morale of the troops or are you trying to boost your own”.
“When he put his arm around me, he groped my right breast,” she said.
“He kept his hand all the way over on my breast,” she said, adding that she felt “embarrassed” afterwards.
“And I remember thinking – is he going to move his hand? Was it an accident? Was he going to move his hand? He never moved his hand.
“It was long enough that he should have known if it was an accident. I’m very confident saying that.”
Mr Franken has now been accused of inappropriate touching by five women. Two incidents relate to United Service Organizations tours of the Middle East and Afghanistan.
The accusations came to light after a radio host in California, Leeann Tweeden, wrote an article about how Mr Franken had made unwanted sexual advances during a 2006 military tour to entertain US troops.
Mr Franken “forcibly” kissed her while they rehearsed for a comedy skit to perform before US troops stationed in Kuwait, and also had a photo taken of him appearing to grope Ms Tweeden’s breast as she slept on a military plane.
Mr Franken apologised to her for the photo but said he remembered the rehearsal differently.
Mr Franken also said he did not recall the encounters with the other women, who each said he had touched their buttocks during photo ops.
An editorial in Mr Franken’s hometown newspaper, the Minneapolis Star Tribune. on Monday said Mr Franken’s apology failed the “full candor test” and “he seems to be saying, ‘I’m sorry for what you think I did'”.
“Can one credibly apologise for acts without acknowledging they occurred?” the editorial board asked.
Mr Franken is not the only senior Democratic lawmaker in Washington facing accusations of groping.
Michigan Congressman John Conyers stepped down from a powerful Congressional committee after he was accused by former staff members of touching them, and requesting sexual favours. In a series of tweets, he denied the allegations.
Buzzfeed News revealed last week that he had paid a $27,000 (£20,000) legal settlement with one accuser. Mr Conyers has acknowledged the 2015 payment but denied misconduct.