NEW YORK (AFP) - The US government on Friday (April 8) kept its encryption battle with Apple alive, pressing the high-tech giant to help crack an iPhone in a drug case in New York.

The move by the Justice Department comes after a high-stakes showdown between Apple and the FBI over access to the iPhone of a California gunman came to an abrupt end, when investigators said they had extracted the data on their own.

Key questions thus remain about law enforcement access to devices with strong encryption and how to balance that with user privacy rights - questions that could be answered if the government's appeal in New York goes forward.

"The government continues to require Apple's assistance in accessing the data that it is authorised to search by warrant," Justice Department lawyers told US District Court Judge Margo Brodie in a written filing.

The US Drug Enforcement Agency and the FBI went to court in New York to compel Apple to help it break into an iPhone confiscated in June 2014 from a suspected methamphetamine trafficker, according to court documents.

The US government sought to get Apple to help break into the iPhone under the auspices of the All Writs Act - a 1789 law that gives wide latitude to law enforcement, and the same one cited in the San Bernardino case.

But earlier this year, a lower court judge sided with Apple, saying law enforcement lacked the authority to compel the company to comply.

"The relief the government seeks is unavailable because Congress has considered legislation that would achieve the same result but has not adopted it," US Magistrate Judge James Orenstein wrote.

The ruling signalled that Apple was on sound footing in the separate but similar battle with the US government over being forced to help crack into an iPhone used by one of the shooters in a December shooting rampage in San Bernardino that left 14 dead.

But that case was dropped when the FBI said an unnamed "outside party" had helped it access the data in the shooter's phone.