A U.S. Security Chief warned that ISIS and other terror groups are planning another attack as big as 9/11

She said ISIS is currently in an ‘interim’ period focusing on a much bigger endgame

She stressed that free movement of goods and people means security has to be tightened in individual countries

MI5 director general Andrew Parker warned Britain is facing its worst-ever terrorist threat

ISIS fanatics and other terror groups are planning another massive attack on the scale of 9/11, a top U.S. security chief warned today.

Elaine Duke, Donald Trump’s acting Secretary of Homeland Security, said jihadists were using crude knives and van attacks to keep their members engaged and their finances flowing as they plot another ‘big explosion’ similar to the September 2001 atrocities.

Speaking at the U.S. embassy in London, she said intelligence is pointing to extremists plotting to take down planes to inflict mass civilian casualties.

Duke said ISIS is currently in an ‘interim’ period focusing on a much bigger endgame.

"The terrorist organizations, 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," The security chief, who has served three U.S. presidents, said.

"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."

"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," she added.

Yesterday Duke said the prospect of a terrorist blowing up an airline using a laptop was just one of the threats facing airlines worldwide.

She said the free movement of goods and people means security has to be tightened in individual countries around the world.

When asked how the U.S. is tackling the threat of another 9/11-style atrocity, 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."

Duke warned that the number of home-grown violent extremists, mostly inspired by terrorist organizations, is increasing in the U.S. She said the ability of ISIS militants to put terrorist propaganda on the internet will appeal more and more to extremists as they are pushed out of Syria and Iraq.

Duke said web giants need to do more to detect extremist content online, and one way of doing this could be using the same technology used to identify people in passenger lists.

"Terrorists are strong, they are adaptable and the terrorist threat is the highest it has been since pre-9/11. We have got to have every tool that’s possible," she added.

A total of 2,996 people were killed during the 9/11 attacks when al-Qaeda suicide attackers hijacked planes and flew them into the World Trade Center in New York and the Pentagon in Washington.

Earlier in the day, Duke met the British interior minister Amber Rudd to discuss how to force internet giants to do more to tackle terrorism ahead of the G7 summit.

Following the recent wave of attacks in Manchester and London, police chiefs have said the threat facing the U.K. is a ‘new norm’ that will not change.

Her chilling remarks came 24 hours after MI5 director general Andrew Parker warned Britain is facing its worst-ever terrorist threat in his first major speech since the U.K. was hit by a wave of attacks.

This article has been adapted from its original source.