Sky News reports: Islamic State and the Assad regime in Syria have been colluding with each other in deals on the battleground, Sky News can reveal.

Our exclusive investigation into leaked secret IS files suggests one piece of co-operation was over the ancient city of Palmyra.

The files also show that the militant group has been training foreign fighters to attack Western targets for much longer than security services had suspected.

The revelations underscore fears in the United States that a network of sleeper cells is spread across Europe, avoiding detection, and is planning further Paris- and Brussels-style assaults.

IS defectors, meanwhile, have told Sky News that Palmyra was handed back to government forces by Islamic State as part of a series of cooperation agreements going back years.

New letters obtained by Sky News, in addition to the massive haul of 22,000 files handed over last month, appear to confirm this. [Continue reading…]