A large cache of documents seized from the so-called Islamic State in Syria has revealed thousands of plots to attack Europe and other parts of the world.

The top British commander in the region said more than 10,000 documents and a huge amount of digital data was seized after the militants were driven out of Manbij in northern Syria in August.

Major General Rupert Jones said a “significant” amount of the group’s terrorist operations were orchestrated from, “within the caliphate, critically from within Raqqa and from within Manbij.”

“They were key external operations hubs,” he said. “There is a huge amount of intelligence, documentation, electronic material that has been exploited there that points very directly against all sorts of nations around the world.”

Speaking to reporters at the Al-Assad air base in Iraq, he declined to discuss details of the suspected plots as British security services are currently analysing the material.

General Jones said further, “fresh” intelligence is expected if the coalition retakes the Iraqi city of Mosul, where US-backed Iraqi and Peshmerga forces have launched an offensive.

"It will be a labyrinth of intelligence and we need to get that into the hands of the intelligence agencies," he said.

Attacks either perpetrated or inspired by Islamic State have struck cities across Europe, including Paris, where 130 people were killed in November last year, and Brussels, where 32 people died in March.

Last week, French anti-terror police foiled a terror ring plotting attacks in France.

Seven people were arrested of French, Moroccan and Afghan origin in Marseille and Strasbourg.

French interior minister Bernard Cazeneuve did not reveal the intended target of the plot, but did say "the foiled attack was a co-ordinated attack aiming to target several sites simultaneously".

The US State Department has urged Americans in Europe to be vigilant against a "heightened risk" of terrorism during the Christmas period.