Home Secretary Amber Rudd said on Sunday tech companies should stop offering a “secret place for terrorists to communicate”, after British parliament attacker Khalid Masood was widely reported to have sent encrypted messages moments before he killed four people last week.

Rudd has summoned the Internet companies to a meeting to urge them to do more to block extremist content from platforms like Facebook and Google’s YouTube, but a government spokesman said encryption was also on the agenda.

“The message is the government thinks there is more they can do in relation to taking down extremist and hate material and that is what they are going to be talking about this afternoon,” the prime minister’s spokesman said on Thursday.

“I’d expect encryption to come up but when these talks were agreed it was in relation to extremist material.”

Some smaller tech firms will be at the meeting, another spokesman said, but the list does not include Apple.

Facebook (FB) and Google (GOOG) declined to comment ahead of the meeting. Microsoft (MSFT) and Twitter (TWTR) did not immediately respond to requests for comment.

The U.S. Internet giants have all raced over the past year to show they are doing more to remove extremist material from their sites, but argue that there is no technical silver bullet that can fix the issue.

In December, they agreed with the European Union to create a shared database to help each other speed this process once any one of the companies identifies clearly illegal or inflammatory content.

Rudd said she was “calling time on terrorists using social media as their platform” on Sunday, and she appealed for help from the owners of encrypted messaging apps such as Facebook’s WhatsApp.

Britain is already implementing sweeping new powers for police and security services under the Investigative Powers Act enacted last year.

“This may be just a way to impress on industry that the government means business here,” said James Blessing, chairman of the UK Internet Services Providers’ Association, which represents more than 200 Internet access and hosting firms.

The new law has provisions to force tech firms to help law enforcement agencies bypass encryption, where possible, and keep records of sites their customers visit, updating decades-old surveillance laws.

The government has said it supports the use of encryption in many business and consumer services, but it has also effectively demanded that law enforcement be given privileged access to decode encrypted extremist chatter.

Technical experts are in nearly universal agreement that such back doors into encrypted systems will weaken security for all web users as the openings used by police will eventually be exploited by cybercriminals or foreign spies.

The European Union is also increasing pressure on the U.S. major tech companies.

On Tuesday, EU Justice Minister Vera Jourova said the commission will propose new policies in June to force Facebook, Google, Microsoft and Twitter to make it easier for police to access data.