"Edmund Fitton-Brown, Senior Advisor to the Counter Extremism Project and former Ambassador of the UK to Yemen, told MailOnline: 'ISIS methodically kept itself alive during the height of military and counterterrorism pressure it faced by creating a global structure of mutually supportive regional networks.'

He said those operating out of Afghanistan, East Africa and West Africa have been 'particularly effective'.

'The regional network structure allows for a formerly "remote province" like Khorasan to step up and enable international attacks if it has the capacity to do so.

'That capacity is partly enabled by funds authorised by the leadership in Syria.

'Khorasan is also important because of diasporas: Uzbek, Chechen, Daghestani and especially Tajik.

'These ethnicities provide networks that link Afghanistan, Turkey, Central Asia, the Caucasus with target venues in Russia, Iran, Germany, Scandinavia, France.'"