The US Department of Justice has opened another legal front in the ongoing war over easy-to-use strong encryption.

According to a Saturday report in The New York Times, prosecutors have gone head-to-head with WhatsApp, the messaging app owned by Facebook. Citing anonymous sources, the Times reported that "as recently as this past week," federal officials have been "discussing how to proceed in a continuing criminal investigation in which a federal judge had approved a wiretap, but investigators were stymied by WhatsApp’s encryption."

The case, which apparently does not involve terrorism, remains under seal.

The government could pursue a strategy similar to the one it has employed in the ongoing terrorism investigation in San Bernardino, in which it was granted a court order that would compel Apple to create new software to defeat the encryption on a seized iPhone. Apple has vowed both publicly and in court papers to fight that order as intensely as possible, citing security concerns.

The Times noted that over the last year, WhatsApp has been upgrading encryption for messaging and voice calls.

As Ars reported earlier this month, all WhatsApp messages sent between Android devices are end-to-end encrypted since late 2014. That means not even parent company Facebook can access the plaintext contents of such messages. (WhatsApp messages that involve an iOS device began using encryption as of August 2015.)

Two years ago, WhatsApp upgraded its security after partnering with Open Whisper Systems, a company founded by Signal creator and well-known security researcher Moxie Marlinspike. During fiscal year 2014, Open Whisper Systems received $900,000 from the Open Technology Fund, an umbrella group whose primary funder is the United States government. That funding came primarily through the Broadcasting Board of Governors and the Department of State.

Matt Steinfeld, a Facebook spokesman, e-mailed Ars on Saturday: "Sorry, we’re declining comment on this." Similarly, Department of Justice spokeswoman Emily Pierce also declined comment.