U.S. law enforcement agencies have seized the sex marketplace website Backpage.com as part of an enforcement action by the Federal Bureau of Investigation, according to a posting on the Backpage website on Friday.

Groups and political leaders working to end forced prostitution and child exploitation celebrated the shutdown of Backpage, a massive ad marketplace that is primarily used to sell sex. But some internet and free speech advocates warned the action could lead to harsh federal limits on expression and the press.

The website posting said U.S. attorneys in Arizona and California, as well as the Justice Department's section on child exploitation and obscenity and the California and Texas attorneys general had helped shut down the website.