Isis scientists and weapons experts have developed sophisticated new weaponry capable of shooting down passenger jets, it has been revealed.
Newly emerged footage shows militants at the group's Syrian base in Raqqa creating a homemade thermal battery, for use in decommissioned military surface-to-air missiles.
Experts say terror groups have had access to such weapons for decades - but storing them and creating the thermal battery vital to the missile's function is very difficult without advanced knowledge.
Kim Sengupta, the Independent’s defence correspondent, said the development was especially significant.
“After the US and UK entered Afghanistan in 2001, there were fears that Stinger missiles given by the Americans to the Afghan Mujaheddin to shoot down Russian aircraft may be used by the Taliban against the Western forces" he said.
“That never came to pass because the missiles’ batteries had a limited shelf life and the Taliban were not able to find a way around that. If Isis has developed a process that enables them to replace these batteries, that will obviously be of major concern.”
It is now feared that with access to this kind of battery, Isis could potentially be capable of recommissioning thousands of disused missiles.
The missiles shown in the footage obtained by Sky News are said to be 99 per cent accurate once they have locked on to their targets.
Concerns that Isis could use abandoned or outdated western military equipment were raised in 2014, after it was reported that Isis had captured vehicles, firearms and even missiles from the US-armed Iraqi army during their advances in Iraq.
Other footage, which Sky News says was passed to them by Free Syrian Army (FSA) fighters who took it from a captured Isis trainer in Turkey, apparently also shows the testing of a full-sized remote-controlled car.
It goes on to show the militants with mannequins fitted with systems that produce a human heat signature - allowing the cars to slip through sophisticated security scanning machines and launch bomb attacks on high-profile targets.
The hours of collected footage also includes training videos designed to instruct jihadis how to launch these kinds of attacks in their own countries.
Major Chris Hunter, a former British Army bomb disposal technician and now counter-explosives expert said the footage was "one of the most significant intelligence finds" in terms of Isis.
"What we've seen with their typical propaganda videos is they're very, very high quality. They're designed, they're produced to inspire people and prospectively touch the nerves of anybody who is viewing them, they're done a very specific way," he said.
"With this training footage it's very clearly purely designed to pass on information - to pass on the progress in the research and development areas - and it gives us a very good insight into where they are now, what they're aspiring to do and crucially the diversity of the types of threats we might face."
Sky News said it had alerted the security services about the footage.
Join our commenting forum
Join thought-provoking conversations, follow other Independent readers and see their replies