LONDON (Reuters) - OpenAI Chief Executive Sam Altman has denied sexually abusing his sister when she was a child, after she filed a lawsuit in the United States accusing him of regularly sexually abusing her between 1997 and 2006.

The lawsuit, filed by Ann Altman's lawyers in a U.S. District Court in Missouri, alleges counts of sexual assault and sexual battery which began when she was three and her brother was 12. It alleges the abuse continued once he became an adult and while she was still a minor.

"All of these claims are utterly untrue," Sam Altman said in a joint statement with his mother and two brothers published on X on Jan. 7. Reuters requested comment from Altman and the law firm representing his sister, but they were not immediately reachable outside of business hours.

Sam Altman, one of the co-founders of OpenAI alongside Elon Musk and others, has become one of the world's biggest tech names since the launch of OpenAI's ChatGPT tool in 2022. He is estimated to be worth over $1 billion, according to Forbes.

His sister's lawsuit seeks damages in excess of $75,000, punitive damages, and for the costs of the lawsuit. It also requests a jury trial.

The lawsuit stated that as a result of the abuse she alleges, Ann Altman had suffered post-traumatic stress disorder, severe emotional distress, mental anguish, and depression, which was expected to continue into the future.

In the statement from Sam Altman and family members, they detailed the financial and medical support the family had tried to provide to Ann, 30.

"Caring for a family member who faces mental health challenges is incredibly difficult," the family's statement said.

Reuters sought comment from Ann Altman's lawyer on the family's statement but did not immediately receive a response.