Apple says that the US government is making "desperate" and "unsubstantiated" accusations to "smear" the company, the BBC reports.
The Department of Justice (DoJ) has been pressuring Apple to give it access to data from the phone used by one of the San Bernardino attackers. While Apple claims that such a demand is "unprecedented," but the DoJ says that Apple has previously provided a similar service to the Chinese government.
The attackers, married couple Syed Rizwan Farook and Tashfeen Malik, killed 14 people in California last December.