A fresh wave of advertisers suspended commercials on YouTube after their ads showed up next to videos that appeared to attract pedophile viewers.

The backlash Friday was the latest over what critics say is the inability of YouTube owner Google, and parent Alphabet Inc., to effectively police the video service and assure advertisers their spots won’t end up accompanying inappropriate or offensive content.

Big brand advertisers, including candy maker Mars Inc., sportswear firm Adidas AG, alcohol giant Diageo PLC and British satellite-TV operator Sky PLC’s Now TV subsidiary, said they had stopped advertising on YouTube. They responded after the Times of London reported that ads for those companies were popping up next to videos of young children, many of which drew lewd comments from viewers.

Other recent reports in the news and on social media have highlighted YouTube videos with millions of views that exploit children by putting them in compromising or predatory situations.

A spokesman for YouTube said Friday that the video-sharing service forbids videos and comments that sexualize or exploit children, and that the videos in question should never have displayed any ads. “We are working urgently to fix this,” the spokesman said.