Attorney General William Barr is set to make the request in an open letter to Facebook CEO Mark Zuckerberg on Friday. Acting Homeland Security Secretary Kevin McAleenan, UK Home Secretary Priti Patel and Australian Minister for Home Affairs Peter Dutton also signed the draft letter, which BuzzFeed News and the New York Times obtained before publication. The US and the UK will reportedly announce a data-sharing agreement alongside the release of the letter.

In March, Facebook announced plans for a more privacy-focused approach to its services. It's also working towards unifying messaging across WhatsApp, Instagram and Messenger with end-to-end encryption.

Barr and the other signees are concerned that end-to-end encryption will hamper law enforcement from tackling illegal activity that occurs through Facebook's messaging platforms. That includes child sexual exploitation, terrorism and election meddling. Earlier this week, a NYT report indicated there were almost 12 million reports of child sexual abuse material on Messenger last year.

The letter argues Facebook should "enable law enforcement to obtain lawful access to content in a readable and usable format," effectively providing authorities with backdoor access to messaging across WhatsApp, Instagram and Messenger. It will ask Facebook to work with governments to ensure that's the case.

It also urges Facebook and other companies to "embed the safety of the public in system designs, thereby enabling [Zuckerberg] to continue to act against illegal content effectively with no reduction to safety, and facilitating the prosecution of offenders and safeguarding of victims."

Update (10:26PM ET): The Department of Justice released both the copy of the letter, and officially announced the US and UK cross-border data agreement. Notably however, they did not release the actual text of the agreement itself, saying "We anticipate releasing a copy of the agreement in the near future following Congressional and Parliamentary notification."

US-UK cross-border data agreement announcement from DOJ: