Islamic State militants are developing their own social media platform to avoid security crackdowns on their communications and propaganda, the head of the European Union's police agency said today.

Europol Director Rob Wainwright said the new online platform had been uncovered during a 48-hour operation against Internet extremism last week.

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"Within that operation it was revealed IS was now developing its very own social media platform, its own part of the Internet to run its agenda," Wainwright told a security conference in London. "It does show that some members of Daesh (IS), at least, continue to innovate in this space."

During a Europol-coordinated crackdown on IS and al Qaeda material, which involved officials from the United States, Belgium, Greece, Poland, and Portugal, more than 2,000 extremist items were identified, hosted on 52 social media platforms.

Jihadists have often relied on mainstream social media platforms for online communications and to spread propaganda, with private channels on messaging app Telegram being especially popular over the past year.

Technology firms, such as Facebook and Google, have come under increasing political pressure to do more to tackle extremist material online and to make it harder for groups such as Islamic State to communicate through encrypted services to avoid detection by security services.

However, Wainwright said that IS, by creating its own service, was responding to concerted pressure from intelligence agencies, police forces and the tech sector, and were trying to found a way around it.

"We have certainly made it a lot harder for them to operate in this space but we're still seeing the publication of these awful videos, communications operating large scale across the Internet," he said, adding he did not know if it would be technically harder to take down IS's own platform.

Wainwright also said he believed that security cooperation between Britain and the EU would continue after Brexit, despite British warnings it is likely to leave Europol and cease sharing intelligence if it strikes no divorce deal with the bloc.

"The operational requirement is for that to be retained. If anything, "If anything we need to have an even more closely integrated pan-European response to security if you consider the way in which the threat is heading," he said.

Europe, he added, is facing "the highest terrorist threat for a generation".

However, Wainwright said there were important legal issues that would have to be thrashed out and it was not easy "to just cut and paste current arrangements".

"The legal issues have to be worked through and then they have to be worked through within of course the broader political context of the Article 50 negotiations (on Britain's planned exit from the EU)," he said.

"In the end I hope the grown-ups in the room will realise that ... security is one of the most important areas of the whole process. We need to get that right in the collective security interest of Europe as a whole, including of course the United Kingdom."