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ISIS is plotting a 'new 9/11' and will bring down planes to cause maximum devastation, according to Trump's Homeland Security chief.

What's more, the terror group is currently using van attacks - like the one at London Bridge - to keep their members engaged while they raise funds for a 'big explosion'.

Elaine Duke, acting Secretary of Homeland Security says the plan is to recreate the 2001 atrocities where four planes were hijacked by al-Qaeda - two of which were crashed into the North and South towers of the World Trade Center.

Speaking at the US embassy in London, Mrs Duke said: "The terrorist organisations, be it ISIS or others, want to have the big explosion like they did on 9/11 . They want to take down aircraft, the intelligence is clear on that.

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"However, in the interim they need to keep their finances flowing and they need to keep their visibility high and they need to keep their members engaged, so they are using small plots and they are happy to have small plots."

She added: "Creating terror is their goal and so a van attack, a bladed weapon attack, causes terror and continues to disrupt the world – but does not mean they’ve given up on a major aviation plot."

Mrs Duke went on to add that terrorists could use a laptop to blow up an aircraft - and is just one of many threats facing airlines all over the world.

She added that it was important to target terrorists in their homes, keep them moving and fearful of attack, therefore allowing them less time to sit and work on bigger plots.

(Image: Reuters)

She said: "We have worked on some strong measures that we can’t talk about. We are trying to play the away game and that is working against them in their terrorist safe havens and homes.

"We do have some terrorist groups on the move, you just saw the take-over of Raqqa and so if we can keep them declining and moving they have less time to sit and prepare."

She also called on technology firm to act more quickly to remove online propaganda which she says has fuelled a rise in homegrown extremism.

The United States and Britain will push social media firms at a meeting of G7 interior ministers this week to do more on the issue, Duke told reporters in London where she had been meeting British Home Secretary Amber Rudd .

(Image: Reuters)

(Image: Ron Agam/Getty Images)

Authorities say propaganda from Islamic State has played a major part in radicalising people in the West but despite its defeat in its capital Raqqa in Syria, Duke said the group's online presence was likely to increase.

"I would surmise being able to put terrorist propaganda on the internet might become more imperative," said Duke, who described the terrorist threat to the United States as being as high as it had been since pre-9/11.

She also warned that those who turned to violence by being radicalised by such material posed a bigger problem than the comparatively small number of fighters who had joined the militant group returning to United States.

"The number of foreign fighters we have returning is declining," she said. "The number of home-grown violent extremists, most of them inspired by terrorist organisations, is increasing."