Morten Storm has seen deep inside the conflict between jihadists and Western intelligence services, having served both.
He was a Danish petty criminal who converted to Islam in the 1990s and became embroiled in the global jihadist network, before abruptly losing his faith and turning against his former friends.
Storm, 39, has emerged from his experiences with a strong conviction that Muslim communities need to be at the forefront of efforts to tackle radical Islam.
He was speaking in Paris, where his book "Agent Storm: My Life Inside Al-Qaeda and the CIA" is about to be released in French.
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He said claims by Western governments that attacks such as those in Paris and Copenhagen this year had nothing to do with Islam "made a mockery" of those who were fighting for a more tolerant version of the religion.
"The silence of the majority of Muslims who are not doing anything about ISIS could lead to a war throughout the Middle East," said Storm, referring to the Islamic State group based in Syria and Iraq.