Warner, the top-ranking Democrat on the panel, said the companies' efforts to address the problem were inadequate.

"The bad news, I’m afraid, is that there is a lot of work still to do. And I’m skeptical that, ultimately, you’ll be able to truly address this challenge on your own. Congress is going to have to take action here," he said.

Top Facebook and Twitter executives were testifying at a committee hearing about foreign entities' use of social media to influence U.S. political discourse.

Warner also said that he was deeply disappointed that Google did not send a top official to the hearing.

(Reporting by Diane Bartz; Editing by Jeffrey Benkoe)