A US ambassador nominated by President Donald Trump who provided key testimony in his impeachment hearings was accused Wednesday of sexual misconduct by three women.

Gordon Sondland, the US envoy to the European Union, denied the allegations, with his lawyer alleging that the accusers were trying to taint his credibility in the inquiry.

The Portland Monthly published named accounts by three women who said that Mr Sondland, a wealthy hotel owner from Seattle, retaliated against them professionally after they rejected him sexually.

One of the women, Jana Solis, said she met Mr Sondland in 2008 when she was seeking work in her position as a safety expert for hotels.

She said Mr Sondland met her for lunch and offered her a job as "my new hotel chick" before slapping her bottom.

She said Mr Sondland later invited her to his Portland home to evaluate his personal art collection - which included a picture of himself with then president George W Bush - and that he exposed himself in the pool house.

She said Mr Sondland at a later meeting also forcibly kissed her. Another woman, Nicole Vogel, said she met Mr Sondland in 2003 over dinner to seek investment in a new magazine.