The department also says Apple designs its products to allow technology 'rather than the law' to control access to critical data.

Prosecutors also made clear that Apple would be allowed to retain possession of the phone and technology.

The motion offers a sharply worded response to a message that Apple's chief executive officer, Tim Cook, said in a message to Apple customers this week.

It represents a further escalation in a public relations battle that the two sides are waging.

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