Apple is due to face the FBI in court later this month. The company, which has said it would have to create software to allow investigators to crack the phone, has argued that doing so could create a dangerous precedent. In a call with reporters Thursday, Apple senior vice president and general counsel Bruce Sewell said the DOJ has become "so desperate" that it has "thrown all decorum to the wind.
"The tone of the brief reads like an indictment," he said.
Sewell called the brief an "unsupported, unsubstantiated effort to vilify Apple." In the call, attorneys for Apple said they plan to file a reply brief, which is due March 15. The attorneys reiterated Apple's position that the disagreement should not be settled in the court system.
Authorities claim they only seek to unlock the device in question. The DOJ reiterated that point Thursday, calling the court order "modest" and arguing it "invades no one's privacy."
"It applies to a single iPhone, and it allows Apple to decide the least burdensome means of complying," the filing said.
Attorneys for Apple questioned Thursday where the limits of the power will stop. Some critics of the court order believe it could lead to a so-called back door through Apple's encryption system. The DOJ contended the case would not give it that power.
Apple, by keeping close control over its software and devices, "maintains a continued connection to its phones," the DOJ's filing said.
"Apple is not some distant, disconnected third party unexpectedly and arbitrarily dragooned into helping solve a problem for which it bears no responsibility," the DOJ wrote.
Many prominent technology companies have backed Apple in the case. Amazon.com, Alphabet's Google, Facebook and Microsoft, among others, recently filed a joint brief in support of Apple.
President Barack Obama will not discuss the dispute on Friday during his keynote address at the South by Southwest music and technology conference, Reuters reported, citing a White House official.
— Reuters contributed to this report.