Attorney General Eric H. Holder Jr. said on Tuesday that new forms of encryption capable of locking law enforcement officials out of popular electronic devices imperil investigations of kidnappers and sexual predators, putting children at increased risk.

“It is fully possible to permit law enforcement to do its job while still adequately protecting personal privacy,” Holder said at a conference on child sexual abuse, according to a text of his prepared remarks. “When a child is in danger, law enforcement needs to be able to take every legally available step to quickly find and protect the child and to stop those that abuse children. It is worrisome to see companies thwarting our ability to do so.”

In his comments, Holder became the highest government official to publicly chastise technology companies for developing systems that make it difficult for law enforcement officials to collect potential evidence, even when they have search warrants. Though he didn’t mention Apple and Google by name, his remarks followed their announcements this month of new smartphone encryption policies that have sparked a sharp government response, including from FBI Director James B. Comey last week.

Federal, state and local law enforcement officials have complained loudly that the companies are undermining efforts to fight crime, including terrorism. Apple’s newest mobile operating system, iOS 8, is so thoroughly encrypted that the company says it cannot unlock iPhones or iPads that use it. Google’s Android operating system plans to begin using encryption automatically, for all users unless they specifically opt out, in a version to be released in October. (It will take months or years for that feature to reach most Android users.)

Company officials have said stronger encryption better protects the privacy of users by toughening the security of the devices against a wide range of intrusions, by governments, criminals or curious hackers. American technology companies have been particularly eager to demonstrate their commitment to user privacy in the aftermath of the revelations by former National Security Agency contractor Edward Snowden, detailing the extensive reach of government surveillance. Apple and Google did not respond to requests for comment Tuesday.

Holder was speaking to the Global Alliance Against Child Sexual Abuse Online, meeting in Washington, when he raised the issue of preserving government access to electronic devices.

“Recent technological advances have the potential to greatly embolden online criminals, providing new methods for abusers to avoid detection,” Holder said. “In some cases, perpetrators are using cloud storage to cheaply and easily store tens of thousands of images and videos outside of any home or business – and to access those files from anywhere in the world.  Many take advantage of encryption and anonymizing technology to conceal contraband materials and disguise their locations.”

He called on companies “to work with us to ensure that law enforcement retains the ability, with court-authorization, to lawfully obtain information in the course of an investigation, such as catching kidnappers and sexual predators.”

Even with the new forms of encryption, government officials maintain access to several sources of data related to the use of smartphones, including the records of calls and texts kept by cellular carriers and the device backups that most smartphones make on remote cloud services, such as Apple’s iCloud. Police with search warrants also are free to use third-party tools to try to crack the encryption on smartphones or other devices. Courts can potentially order users to furnish passcodes that will unlock devices as well.