The US government is asking for greater access to Apple’s software than even the Chinese government, an Apple executive has said, as the company resists an order forcing it to help the government crack the passcode for a phone that was used by a San Bernardino shooter.

America’s most valuable company and its government used increasingly bellicose tones on Friday in a debate over whether national security can dictate how Silicon Valley makes products.

On 16 February, a federal judge ordered Apple to assist the FBI in accessing the phone.

Apple has refused, arguing that to do so would set a legal precedent that could force it to hack a suspect’s phone each time authorities face a warrant. It argues that would violate user trust, privacy norms and weaken the core security of the company’s flagship smartphone.

Early Friday, the Justice Department released a lengthy legal filing that accused Apple of misinterpreting the law and placing marketing goals over national security.

Apple’s legal team was huddled Friday preparing a response and declined to speak on the record. But in several calls with reporters, a senior Apple executive agreed to offer some response on the condition of anonymity and that reporters not quote the executive’s exact words.

The company’s executive said that the Justice Department’s request was so unprecedented that no other country – specifically mentioning China – had asked for similar access. That comes following reports that the country, a huge market for Apple, has asked to inspect western technology products for “security”.

The company executive also said it was safe to assume that Apple would continue to add more security features to its products to make it harder still for investigators to get access.

The company’s latest spat with the FBI goes back to the fall of 2014, when Apple expanded the default use of encryption on its newer iPhones. At the time, it said it would no longer be able to retrieve passcodes used to unlock phones for federal agents.

The FBI conceded this week it can’t force Apple to give it the passcode, but it concocted a clever workaround. It persuaded a judge to order Apple to make it easier to guess the passcode by weakening other countermeasures.

On the call Apple acknowledged that, on a technical level, the workaround could be applied to any iPhone. Authorities would have to get a warrant for each of those cases.

In its filing Friday, the government said that it had tried several other ways to access gunman Syed Farook’s phone, which was owned by his employer – the county agency he targeted. One of them would have been to return his iPhone to his home wireless network to see if it would automatically back up its files on Apple’s iCloud service.

This potentially could have given investigators access to Farook’s files and iMessages up to the moment of the attack.

However, Apple and federal agents discovered that option wouldn’t work. In the hours after the shooting, San Bernardino county staff tried to access Farook’s iCloud account and reset his password. This, unintentionally, triggered an Apple security measure that made it impossible to back up the phone.

The Apple executive conceded there is no way to know if this would have worked. It’s possible, as the government argues, that Farook had turned off the auto-update function. The phone last updated on 19 October, some six weeks before the shooting.

Apple has until 26 February to file a response in federal court.