The website Backpage.com was taken down Friday and seized by federal law enforcement authorities, according to a notice posted online.

The classifieds website has been the focus of intense scrutiny over the issue of its sex ads, which have included those involving children being trafficked by adults. A Washington Post investigation last year found that Backpage was using a contractor in the Philippines to contact prostitutes on other websites, seeking to lure their ads to Backpage and creating the ads for those prostitutes in advance.

Visitors to the site on Friday were greeted with an announcement that said “backpage.com and affiliated websites have been seized as part of an enforcement action” by agencies including the FBI as well as the law enforcement wings of the U.S. Postal Service and the Internal Revenue Service.

Numerous other state and federal authorities in Arizona, California and Texas were also “participating in and supporting the enforcement action,” the notice stated. It said more information would be released later Friday by the Justice Department; a spokesperson did not immediately respond to a request for comment.

Since Craigslist shut down its “Adult Services” section in 2010, Backpage has attracted greater prominence and income. Embedded within prostitution ads on websites are a certain number of solicitations for children, anti-sex trafficking groups have said.

In 2016, a Senate subcommittee launched an investigation into Backpage’s role in child sex trafficking and found that Backpage modified the wording of ads to delete references to children, while still allowing the ads to stand.

Backpage has denied knowingly facilitating sex trafficking, and has noted that it cooperates with requests from law enforcement to help track down advertisers and victims. Some in the sex worker community have said the site provides them a safe way to meet clients, and that removing the site will make their lives more difficult.

The Senate investigation led to a bill which passed both houses of Congress last month, titled “FOSTA,” an acronym for the Fight Online Sex Trafficking Act. The bill amended the Communications Decency Act and would enable state prosecutors and victims of sex trafficking to pursue website operators in both criminal and civil court. It is awaiting President Donald Trump’s signature.

In court filings last year, Backpage revealed that it was being investigated by a grand jury in Phoenix, where the site was originally launched as part of the New Times alternative weekly newspaper chain.

Local media reports said that the FBI had raided the Arizona home of Michael Lacey, a co-founder of Backpage. The FBI confirmed that “law enforcement activity is occurring” and referred further questions to the Justice Department.