Intelligence obtained by Western security agencies before the November 13 Paris attacks indicated that Abu Mohammed al-Adnani, the head of ISIS' external operations efforts, was the key figure behind the ambitious plot, CNN reported citing a senior European counter-terrorism source.

As many as 60 ISIS fighters had been deployed by the group to Europe to carry out attacks on five cities and had already reached European soil, the source said.

The intelligence indicated that the target cities included Paris, London, Berlin and a major population centre in Belgium. However, there was no indication the plan was to attack the cities simultaneously.

The source cautioned that the threat stream was based on intelligence which was fragmentary and difficult to verify, and it was too vague to act on. In addition, there was no specific intelligence prior to the Paris attack on any moving parts of the plot, the report said.

"In terms of ambition, it also just pointed towards something we already knew. ISIS had hardly made it a secret it sought to target Europe," the source was quoted as saying.

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