An explosion in reports of child sexual abuse imagery on the internet is prompting the authorities to step up pressure on technology companies over their use of encryption — and Facebook, which flags by far the largest amount of the material, is drawing outsize attention.

The tension is part of a growing debate over privacy and policing in the digital age. Law enforcement groups have long lamented the use of encryption, a tool that protects personal data from hackers and government surveillance but also lets child predators and other criminals hide their online activities.

There is increasing “international consensus, at least among law enforcement folks, that this is a serious problem,” said Sujit Raman, an associate deputy attorney general in the Justice Department. “And the companies, you know, they’re just not as engaged on the issue as they really need to be.”

The New York Times reported on Saturday that Facebook Messenger, which is not encrypted, accounted for nearly two-thirds of reports last year of online child sexual abuse imagery. On Wednesday, the Justice Department said that Facebook as a whole was responsible for 90 percent of the reports.