Following the terror attack in London last week, UK Home Secretary Amber Rudd says government intelligence services must be able to access messages from apps like WhatsApp.

"We need to make sure that organizations like WhatsApp, and ... plenty of others ... don't provide a secret place for terrorists to communicate with each other," she said in a video posted by The Guardian. "It used to be that people would steam open envelopes or just listen in on phones when they wanted to find out what people were doing, legally."

The individual responsible for the attack on Westminster Bridge last week reportedly used WhatsApp shortly before carrying it out.

In a statement, a WhatsApp spokesperson said: "We are horrified at the attack carried out in London and are cooperating with law enforcement as they continue their investigations."

WhatsApp and other similar services "cannot get away with saying 'we are a different situation,' they are not," according to Rudd, who has reportedly invited reps from popular messaging services to a March 30 meeting.

Rudd argued for a "carefully thought through, legally covered arrangement" rather than a mandate, but did not rule out legislation if the companies refuse to comply, The Guardian says.

That would likely require WhatsApp to lessen its security and create a backdoor for government officials, something it and its rivals have thus far refused to do. Last year, WhatsApp turned on full end-to-end encryption by default, meaning WhatsApp does not have access to specific messages.

"Every call you make, and every message, photo, video, file, and voice message you send, is end-to-end encrypted by default, including group chats," WhatsApp co-founders Jan Koum and Brian Acton wrote in a blog post at the time. "End-to-end encrypted messages can only be read by the recipients you intend."

WhatsApp is willing to fight government efforts to access user content; it's been blocked twice in Brazil and been locked in a "prolonged standoff" with the DOJ, according to the New York Times.

"Encryption is one of the most important tools governments, companies, and individuals have to promote safety and security in the new digital age. While we recognize the important work of law enforcement in keeping people safe, efforts to weaken encryption risk exposing people's information to abuse from cybercriminals, hackers, and rogue states," Koum and Acton wrote in a 2016 blog post.

Apple faced a similar battle with the FBI following the San Bernardino attack. The feds wanted access to an iPhone 5c owned by one of the shooters, but Cupertino could not comply without creating a backdoor version of iOS that it said would put other iPhone owners at risk. After a very public battle, during which the FBI argued repeatedly that this backdoor mobile OS was the only solution, the agency reportedly ended up hiring a hacker who cracked the device. And that phone ultimately contained no actionable data, according to reports.

Congress also stepped into the fight, with the Senate crafting legislation that would have forced companies like Apple to comply with court orders that demand access to their products and services. That did not move forward, however.