“We are being spied upon by everybody and everywhere,” said Susan Landau, a Tufts University computer security professor. “It is very easy to listen in on communications. Securing data is a clear national security interest.”

The Justice Department and its counterparts in Australia and Britain have long pushed for back doors to other tech platforms but are focusing on Facebook because of Mr. Zuckerberg’s plan to add end-to-end encryption to all of the company’s platforms, a government official said in a background briefing for reporters on Thursday .

Mr. Barr and Britain’s home secretary, Priti Patel, signed a pact late Thursday that eases the legal barriers for American and British law enforcement agencies to request electronic data from tech companies in both countries for investigations into terrorism, child sexual abuse and other crimes. Under the current system, such requests can take up to two years to process.

Facebook has also become a focus of law enforcement’s push against encryption because of the role it could play in the spread of online child sexual abuse images if it were extended to its Messenger platform, The Times reported on Wednesday.

Facebook’s dominant position and huge user base across its platforms make it a tempting target for the Trump administration as it begins a renewed push against end-to-end encryption.

In Washington and around the world, there has been an aggressive antitrust push against the big tech companies. President Trump has repeatedly railed against Facebook, Twitter and other companies, claiming that they have inhibited conservatives’ speech.

In recent weeks, Facebook has taken steps to mend fences in Washington. Mr. Zuckerberg and Sheryl Sandberg, the company’s chief operating officer, have made trips to Capitol Hill, and Mr. Zuckerberg met Mr. Trump for the first time last month, even pausing for a photograph in the Oval Office.