LONDON - One of the U.K.'s top security officials branded ISIS Tuesday an "enduring threat" that has not been eliminated, as he revealed he believes hostage John Cantlie is alive.

In a briefing for journalists in London attended by Fox News, Ben Wallace, the Security Minister, said while the so-called Islamic State has been "massively degraded...it hasn't gone away.

Officials here now estimate some 900 Brits have gone to fight with ISIS in recent years. About half of them were either killed or gave up. The other half are hardened militants still remaining in the Mideast region or in other failed states including Africa. British officials note that the time between radicalization and attacks has shortened thanks to the nature of the internet.

During the briefing, Wallace also said he believes British journalist John Cantlie is alive. Cantlie, a war photographer was captured by the group ‎over six years ago along with American journalist James Foley, who was subsequently beheaded. Cantlie, however, has been used in several propaganda videos. Wallace would not comment on where it's believed Cantlie currently is and any efforts by Britain to free him. The last video to feature Cantlie was released by ISIS in December 2016.

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Wallace's comments come amid reports that two other British ISIS fighters, nicknamed "The Beatles," could face trial in a U.S. court. They allegedly participated in ISIS terror including the videoed executions of American prisoners before being captured. Wallace's Home Office argued for sharing evidence with the U.S. and their transfer but against sending them to Guantanamo.

After somewhat of a lull, Britain was hit by five deadly terror attacks on its soil in 2017. The wave of bloody strikes, which included a suicide bomb attack at the end of an Ariana Grande concert in Manchester, resulting in the deaths of 22 people, was branded a "wake-up call."

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Wallace appeared to regret the decision by the Trump administration to withdraw US troops from Syria.

"Without the coalition there, they are no help to anyone," he said. He also noted the possible loss of information on ISIS activities, adding : "If you don't have 'feet on the ground' you're going ‎to have less intelligence."

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As for the effect on counter-terrorism that the U.K.'s decision to leave the European Union will have, Wallace acknowledged some efforts would be made "sub-optimal." He said the ability for the U.K. to make quick arrests on the European mainland would be lessened, but he also noted Britain will have stronger control of its borders, potentially keeping out would-be threats from the continent.

Still, Wallace believes that cross-border cooperation, especially between the U.K. and the U.S. in dealing with terrorism ‎remains high.

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"It's all about catching the same 'bad guy.'". he said, adding however, there are still a lot of "bad guys" out there.