FBI Director James Comey has warned success against ISIS in the Middle East could lead to more terrorism in the West.

Comey said the destruction of the extremist group's bases in Syria and Iraq would likely mean its remaining forces spread further abroad.

'At some point there is going to be a terrorist diaspora out of Syria like we've never seen before,' Comey said at a cybersecurity conference at Fordham University in New York on Wednesday, according to CNN.

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FBI Director James Comey (pictured) has warned success against ISIS in the Middle East could lead to more terrorism in the West

Comey said the destruction of the extremist group's bases in Syria and Iraq would likely mean its remaining forces spread further abroad (stock image)

'Not all of the Islamic State killers are going to die on the battlefield.'

The FBI Director also said stopping attacks is harder than trying to find a needle in a haystack, before comparing the potential spread to the one seen when al-Qaeda was formed.

'We have to figure out which pieces of hay may become a needle because there are troubled people consuming that propaganda all over the world,' he said.

'This is an order of magnitude greater than anything we've seen before.

'A lot of terrorists fled out of Afghanistan... this is 10 times that or more.

'We saw the future of this threat in Brussels and in Paris.'