FBI Director James Comey is concerned about the new privacy features on Apple and Google devices, although tech companies are still able to hand over cloud storage data to the Police.
Apple devices running iOS 8 will no longer allow user passcodes to be bypassed, which means encrypted iPhones and iPads, will no longer be physically accessible for law enforcement purposes.
Mr Comey told reporters at FBI headquarters in Washington yesterday: "What concerns me about this is companies marketing something expressly to allow people to place themselves above the law."
The latest move from tech companies, follows increased public concerns about US and UK government surveillance in the last year, brought about by the leak of transatlantic government surveillance practices by former NSA worker Edward Snowden in 2013.
Apple, meanwhile, has outlined the new privacy features on its website: "Unlike our competitors, Apple cannot bypass your passcode and therefore cannot access this data – so it's not technically feasible for us to respond to government warrants for the extraction of this data from devices in their possession running iOS 8."
Comey told reporters he understood the need for privacy, but government access to mobile devices may be needed in extreme cases, including in the event of terror attacks.
"Google is marketing their Android the same way: 'Buy our phone and law enforcement, even with legal process, can never get access to it,'" said Comey.
The FBI's latest tech terror concern followed a leaked FBI report earlier this year that detailed the Bureau's fears about driverless cars being possible terror attack tools.
For Google's next release, Android L, encryption will be enabled by default, compared to previous releases where encryption was optional for users. Google spokeswoman Niki Christoff said last week "As part of our next Android release, encryption will be enabled by default out of the box, so you don't even have to think about turning it on."
Tim Cook, Apple Chief told PBS News last week: "People have a right to privacy," which he thinks will be a key topic over the next year or so.