Attorney Alan Dershowitz is swinging back at what he describes as fabricated claims, alleged in a U.S. court document, that he was involved in a prostitution ring connected to the Jeffrey Epstein sex scandal.

The claims against one of the most recognizable names in American law surfaced this week in a lawsuit over a deal that U.S. prosecutors struck with Mr. Epstein, a U.S. financier and former client of Mr. Dershowitz's.

Mr....