Democratic presidential candidate Hillary Clinton called on tech companies Sunday to help "disrupt" the Islamic State online in the wake of last week’s mass shooting in San Bernardino, Calif.

Clinton said at a Washington event that ISIS is “using web sites, social media, chat rooms and other platforms to celebrate beheadings, recruit future terrorists and call for attacks,” and asked Silicon Valley to crack down on the terror group.

The United States needs to hold an “urgent dialogue” with companies such as Google, Twitter and Facebook, said Clinton, and discuss how those “ubiquitous sites” could help keep ISIS quiet online.

ISIS operates a sophisticated digital propaganda machine that often relies on U.S. social media platforms and that has been a challenge for many in Silicon Valley. Many tech companies have tried to remove Islamic State material from their sites by deeming it a violation of their terms of service. Facebook's community standards, for instance, explicitly ban terrorist groups from having a presence on the site. Supporting or praising the leaders of violent groups is also not allowed, the company says.

But tech firms have also had to balance the blocking of inflammatory ISIS rhetoric against free speech and research concerns. Google, for example, has resisted placing a blanket ban on terror-related search results on YouTube, citing the need for “educating people about the dangers and violence” of the group.

Tech companies also face a growing challenge in policing hate speech online: There is an overwhelming amount of it. The industry largely relies on users to report inappropriate content, which is then reviewed by teams of human employees. But even when the firms take the offending material down, it often reappears under a new account that may or may not get reported again. And because social media sites have a mindboggling number of posts to sift through, they need better systems for detecting and weeding out provocative ISIS content, Clinton said.

"We're going to have to have more support from our friends in the technology world to deny them online space," Clinton said.

Clinton’s remarks largely avoided one particular controversial aspect of technology and counterterrorism: the use of encryption to shield online communications from prying eyes.

Some U.S. officials want tech firms to build their systems in ways that would make it easier for authorities to snoop on those secret messages. But Silicon Valley companies such as Apple have pushed back, arguing that the use of “back doors” could also give malicious hackers an easier way to steal innocent users’ personal information.

“It's more complicated with some of what [ISIS does] on encrypted apps,” said Clinton, “and I'm well aware of that. That requires even more thinking.”

The White House this year abandoned a legislative effort to impose encryption back doors on tech companies. But in a speech of his own Sunday, President Obama vowed to put new pressure on “high-tech and law enforcement leaders to make it harder for terrorists to use technology to escape from justice.”