A deadly attack on a French satirical magazine that lampooned Islam seems certain to fuel rising anti-immigration movements around Europe and inflame a "culture war" about the place of religion and ethnic identity in society.

The first reaction in France to Wednesday's killing of 12 people at the offices of Charlie Hebdo by two masked gunmen was an outpouring of support for national unity and freedom of speech.

But that looks likely to be little more than a momentary cease-fire in a country gripped by economic malaise and high unemployment. France has Europe's largest Muslim population and is in the throes of a virulent debate over national identity and the role of Islam.

"This attack is bound to accentuate rising Islamophobia in France," said Olivier Roy, a political scientist and Middle East specialist at the European University Institute in Florence.

A book by journalist Eric Zemmour entitled Le suicide francais (French suicide), arguing that mass Muslim immigration is among factors destroying French secular values, was the best-selling essay of 2014. The publishing event of the new year is a novel by controversial author Michel Houellebecq that imagines a Muslim president winning power in 2022 and enforcing religious schooling and polygamy in France and banning women from working.

The right way

That intellectual ferment has mingled with public anxiety over the radicalization of hundreds of French Muslims who have gone to join Islamic State fighters in Syria and who security officials fear may return to cause carnage in France.

The far-right National Front lost no time in linking the most deadly act of political violence for decades to immigration and calling for a referendum to restore the death penalty, even though a leading French imam, Hassen Chalghoumi, said the right way to counter Charlie Hebdo was not through bloodshed or hate.

Party leader Marine Le Pen, who surveys suggest would top the first round of a poll if a presidential election were held now, said "Islamic fundamentalism" had declared war on France and that demanded strong, effective action.

While she was careful to draw a distinction between Muslim citizens who share French values and "those who kill in the name of Islam", her deputy, Florian Philippot, were less cautious.

"Anyone who says Islamist radicalism has nothing to do with immigration is living on another planet," Philippot said.