The UK government wants there to be "no place for terrorists to hide," and that includes on encrypted messaging services. The company first on its agenda? WhatsApp.

Speaking on the BBC's Andrew Marr Showon Sunday, Home Secretary Amber Rudd called for companies that provide secure communication apps to work with law enforcement.

"We need to make sure that organisations like WhatsApp, and there are plenty of others like that, don't provide a secret place for terrorists to communicate with each other," she said.

"It used to be that people would steam open envelopes or listen in on phones when they wanted to find out what people were doing, legally, through warrantry [sic]. But in this situation, we need to make sure that our intelligence services have the ability to get into situations like encrypted WhatsApp."

Rudd's comment came after media reports on Sunday that the Westminster Bridge attacker had sent a WhatsApp message prior to the incident that cannot be accessed because it was encrypted.

Fifty-two-year-old Briton Khalid Masood used a car and a knife to carry out an attack in the heart of London on Wednesday that left four people dead. He was killed by law enforcement on the scene.

Rudd said she was not arguing for the government to access all messages on such platforms. Instead, she wants encrypted services to recognise they have a responsibility to engage with law enforcement agencies to counter terrorism.

"They cannot get away with saying 'we are a different situation,'" she said. "They are not."

A WhatsApp spokesperson said the company was horrified at the London attack, adding that it is "cooperating with law enforcement as they continue their investigations."

The rhetoric on Sunday highlighted a clash between digital privacy and national security that has been playing out globally in recent years.

The most famous case so far has been Apple's tussle with the FBI. In 2016, the security service took on the Silicon Valley giant in an attempt to bypass the lock screen of the iPhone 5C used by San Bernardino gunman Syed Farook.

Farook and his wife killed 14 people and wounded 22 more in San Bernardino, California in Dec., 2015.

The U.S. Justice Department obtained a court order ordering Apple to assist the FBI in bypassing the phone's security, fearing that too many attempts to guess the passcode would wipe the phone's memory.

Warning that the FBI was seeking a "dangerous power," Apple fought the order, and ultimately the FBI managed to use an undisclosed technique to access the smartphone in question.

Security experts warn that building a backdoor into the iPhone or services like WhatAspp would compromise the safety of users in unintended ways: If UK police can somehow read encrypted messages, for example, what's to prevent law enforcement in countries with a poor human rights record from demanding the same level of access?

The UK-based digital rights advocate Open Rights Group has warned that undermining encryption would make ordinary internet activities more vulnerable.

"Compelling companies to put backdoors into encrypted services would make millions of ordinary people less secure online," the group's executive director, Jim Killock, said in a statement. "We all rely on encryption to protect our ability to communicate, shop and bank safely."

The UK already has extensive laws allowing the government access to the internet footprint of its citizens.

In late 2016, it passed the Investigatory Powers Act, also known as the Snoopers' Charter. The bill creates a quasi-internet history database that's accessible to law enforcement upon request, among other measures.

The Associated Press contributed to this report.