London: An Al Qaida-inspired gunman kills paratroopers and Jewish children in southern France. A far-right fanatic enraged by Muslim immigration guns down dozens of youths at a summer camp in Norway.

Two atrocities in the space of the year, coming from opposite ends of the spectrum, are raising fears across Europe that a growing climate of ethnic and religious hostility is inspiring extremist violence — and creating the conditions for deadly clashes.

On Thursday, French police arrested 19 people in a crackdown on suspected Islamist networks as President Nicolas Sarkozy made the battle against extremism the keynote of his re-election campaign. He said more arrests would follow to get rid of "people who have no business in the country"

Arrests took place in several cities, including Toulouse where extremist gunman Mohammad Merah was shot dead by police last week after a series of cold-blooded shootings that left seven dead, including three Jewish children.

Sarkozy said the arrests targeted "radical Islam" and that the trauma in France after the shootings in Toulouse and nearby Montauban was like that felt in the United States after the September 11, 2001 attacks.

However, the attacks in France and Norway represent the most horrific extremes of two trends of intolerance troubling Europe: strengthening far-right sentiment that has sometimes bled into the mainstream, and growing radicalisation in Europe's disadvantaged, immigrant-heavy neighbourhoods. "These terrorist events are creating sparks, and a small spark can set off a huge fire," said Magnus Ranstorp, research director of the Centre for Asymmetric Threat Studies in Sweden.

"It can set off huge social polarisation, and this is what the terrorists want to achieve. Now there is an increased rightwing climate — the counter-jihad movement — feeding off these Islamophobic forces."

The mood is volatile, Ranstrop said, made more so by the methods of the killers — citing how in France, Merah shot video of his attacks that was mailed to the Al Jazeera television network.

"You have the counter-jihad movement, and on the other side you have an old Al Qaida structure giving out directives for people to carry out their own personal jihads by solo terrorist activity. The manner in which you carry out these attacks matters: Recording them, sending films to Al Jazeera, shooting people execution style, all to create polarisation and revulsion, to create an overreaction."