Craigslist said on Wednesday that it had permanently closed the section of its sites in the United States that carried sex-related advertising, but it defended its right to carry such advertisements as well as its efforts to fight sex trafficking.

The company abruptly removed links to the ads for sexual services earlier this month and replaced them with a black label bearing the word “censored.” Until Wednesday it had not explained its move.

William Clinton Powell, director of customer and law enforcement relations at Craigslist, and Elizabeth L. McDougall, a partner at Perkins Coie, Craigslist’s law firm, discussed the change in testimony at a hearing on sex trafficking of minors before the House Judiciary Committee in Washington.

“Craigslist discontinued its adult services section on Sept. 3, 2010, and there are no plans to reinstate the category,” Mr. Powell said. “Those who formerly posted ads in the adult services category will now have to advertise elsewhere, and in fact there is evidence that this process began immediately.”