Updated

The U.K. government wants WhatsApp to give security services access to encrypted messages in the aftermath of the Westminster Bridge terror attack. Officials, however, could face stiff challenges if they choose to apply U.K. surveillance legislation to the U.S.-based firm, according to a digital privacy advocate.

British press reports suggest Westminster Bridge attacker Khalid Masood used the WhatsApp messaging service just minutes before the Wednesday rampage that left three pedestrians and one police officer dead and dozens more wounded.

Home Secretary Amber Rudd used appearances on BBC and Sky News Sunday to urge WhatsApp and other encrypted services to make their platforms accessible to intelligence services and police trying to carrying out lawful eavesdropping.

APPLE DENIED MASSIVE ICLOUD HACK

“We need to make sure that organizations 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, in a BBC interview. “We need to make sure that our intelligence services do have the ability to go into situations like encrypted WhatsApp.”

Last year the U.K. passed the Investigatory Powers Act, which aims to strengthen the country’s surveillance powers.

However, the London-based Open Rights Group, which advocates for digital privacy and free speech online, told Fox News that any attempt to apply U.K. surveillance legislation would take the government into uncharted legal waters.

"The U.K. claims the power to ask companies with U.K. users to change their products as long as it is reasonable or technically feasible,” explained Jim Killock, Open Rights Group executive director, in a statement emailed to Fox News. “Although WhatsApp is U.S.-based, its parent company, Facebook, has offices and assets in the UK -- and so it might be compelled to respond to such a request. However, none of this is tested in law; we don’t know whether there would be resistance or if the U.S. government might try to intervene.”

TRACTOR HACK: FARMERS ARE HARNESSING HACKED SOFTWARE FOR JOHN DEERE REPAIRS

WhatsApp, which is owned by Facebook, says that it is working with U.K. authorities following Wednesday’s attack. “We are horrified at the attack carried out in London and are cooperating with law enforcement as they continue their investigations,” it said, in a statement emailed to Fox News.

In an interview with Sky News, Rudd said that tech giants such as Facebook, Google and Twitter need to step up in the battle against terrorism. “They really have to take responsibility for the fact that their sites, their platforms, their publishing enterprises, are being used by terrorists,” she said.

The Cabinet Minister is meeting with key players in the tech industry on Thursday and will urge them to play a bigger role in tackling terrorists.  “I want them to be part of this answer,” she said, but would not rule out changes to the law, if needed. “I am not taking anything off the table,” she added.

MILITARY PERSONNEL DATA LEAKED IN DUN & BRADSTREET DATABASE

The tech industry has faced previous law enforcement demands for access to data after major attacks. In the United States, Apple fought the FBI's request for the passcodes needed to unlock an iPhone that had been used by one of the perpetrators in the deadly 2015 extremist attack in San Bernardino, Calif.

The FBI initially claimed it could obtain the data only with Apple's help, but ultimately found another way to hack into the locked phone.

Controversy has swirled around WhatsApp before. Judges in Brazil, for example, blocked the messaging app on three occasions amid rows over handing over messages to the courts.

FOR THE LATEST TECH FEATURES FOLLOW FOX NEWS TECH ON FACEBOOK

The Westminster Bridge attack has thrust secure messaging apps firmly into the spotlight again. ISIS sympathizers cheered the attack using channels in the Telegram app. ISIS used Telegram to claim credit for the Paris terror attacks in November 2015, prompting the messaging app to remove a slew of ISIS-related channels.

The Associated Press contributed to this article.

Follow James Rogers on Twitter @jamesjrogers