After an artist accused the painter Kehinde Wiley of sexual assault in an Instagram post on Sunday, Mr. Wiley denied the allegations, saying on his own Instagram account that “someone I had a brief, consensual relationship with almost three years ago is now making a false accusation about our time together.”

“These claims are not true and are an affront to all victims of sexual abuse,” Mr. Wiley added.

Mr. Wiley, who was born in Los Angeles, is one of the best known painters in the United States, and is famous for his 2018 portrait of President Barack Obama.

On Sunday, Joseph Awuah-Darko, a British-born Ghanaian artist and the founder of the Noldor Artist Residency in Ghana, said in a lengthy Instagram post that on June 9, 2021, Mr. Wiley assaulted him twice during and after a dinner in Ghana that was held in the famed artist’s honor. In the first incident, Mr. Awuah-Darko said that he had been directing Mr. Wiley to a washroom when the star suddenly grabbed his buttocks.

Later that evening, Mr. Awuah-Darko said, a second assault occurred that was “much more severe and violent.” Mr. Awuah-Darko did not give further details of that incident on Instagram, but in a telephone interview, he said that a sexual encounter began consensually, but that it then moved to a bedroom, where he says that Mr. Wiley forced himself on him after Mr. Awuah-Darko had said he did not want to go further.

Mr. Awuah-Darko showed The New York Times text exchanges he said he had with Mr. Wiley from after their encounter, in which he repeatedly told Mr. Wiley that he was missing him and said he wanted to meet again. Mr. Awuah-Darko said that he had initially convinced himself that his encounters with Mr. Wiley had been loving. It was only in the fall of 2023, after therapy, that he admitted to himself that the incidents had been assaults and told a friend what had happened.

“I am aware I’m not the perfect sexual assault victim,” Mr. Awuah-Darko said, “but this is what happened to me. I’m hoping other people come forward.”

In an emailed statement, Mr. Wiley said that Mr. Awuah-Darko had “been trying to be part of my life ever since we met. He flew to Nigeria to attend my birthday party, attempted to visit my home in upstate New York, sent me warm and cordial text messages, and attended my exhibition at the de Young Museum in San Francisco almost a year ago, posting on Instagram that the show by his ‘dear friend’ was ‘breathtaking.’”

On Sunday, Mr. Wiley’s lawyers sent Mr. Awuah-Darko a cease and desist letter, shared with The Times, demanding that the Ghanaian artist delete his Instagram posts and refrain from making what it said were false statements against Mr. Wiley. Mr. Awuah-Darko said Sunday that he had not seen the letter.

No criminal charges have been filed against Mr. Wiley; Mr. Awuah-Darko said the accusations would not be handled well in Ghana, where the Parliament passed a bill in February that would impose jail terms on people who identify as L.G.B.T.Q. or organize gay advocacy groups.