Major-General Rupert Jones, the deputy commander of US-led operations against the militants, said the files had been retrieved in July by Western-backed Kurdish and Arab militias from the former Islamic State (ISIS) stronghold of Manbij, in the Aleppo governorate of northern Syria.
Jones toldsome British newspapers that an even bigger haul of data about ISIS was expected to be uncovered in the terrorists' stronghold of Mosul, in northern Iraq, which he predicted would fall by the early half of next year.
"I am absolutely certain that an extraordinary amount of intelligence will come out of Mosul. We have ramped up as a coalition our ability to gather and process all that intelligence, because it will be a labyrinth of intelligence and we need to get that into the hands of intelligence agencies," he said.
While specific plots against Britain had not yet emerged, he said he was in no doubt that ISIS, also known by its Arabic acronym Daesh, remained a threat.
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Heavy fighting continues in Mosul where Iraqi security forces began an assault to drive out ISIS nearly six weeks ago.
The upcoming struggle for Raqqa will be worse, Jones predicted.
"What we are now in the process of doing is starting the isolation of Raqqa. For as long as Raqqa is sitting there, they can orchestrate external operations. So the sooner it's liberated or the sooner Daesh are liberated from there, the better," he said.