Francois Molins said that French security services had identified 416 French donors to IS and had also detected 320 fundraisers mainly based in Turkey and Libya who transferred the money to the jihadists.

A two-day conference on combating the financing of terror groups began Wednesday at the Organization for Economic Cooperation and Development (OECD) bringing together around 80 ministers and 500 experts.

French President Emmanuel Macron will close the event with a speech later Thursday.

Attacks on Western targets have become increasingly low-cost since the 9/11 atrocities in the United States in 2001, particularly in recent years when followers of Islamic State (IS) have often used only vehicles or automatic weapons to kill people.

But Molins estimated that attacks in France in January 2015 targeting the Charlie Hebdo magazine and a Jewish supermarket would have cost 25,000 euros ($30,000).

More deadly assaults by teams of IS jihadists in Paris in November of that year, including against the Bataclan concert hall, would have cost an estimated 80,000 euros, he said.

A French presidential official briefing journalists ahead of the terror funding conference this week said that IS income was estimated at about one billion dollars (820 million euros) a year between 2014-2016.

Most of this was from local taxation, oil revenues and looting, with far smaller amounts flowing in from overseas donors.

French officials are concerned that the money has been transferred out of Syria and Iraq and could be used to rebuild the organisation.

"It has been moved since, at least in part. It's probably somewhere," the official said on condition of anonymity. "These groups are very skilful in using sophisticated techniques to move financial resources around."