French police swooped down on suspected Islamist networks on Friday, arresting 19 people as President Nicolas Sarkozy vowed a crackdown would continue after an extremist gunman's killing spree.

The arrests took place in several cities including Toulouse, where Mohamed Merah was shot dead by police last week after a series of cold-blooded shootings in southwestern France that left seven dead.

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

"What must be understood is that the trauma of Montauban and Toulouse is profound for our country, a little - I don't want to compare the horrors - a little like the trauma that followed in the United States and in New York after the September 11, 2001 attacks," he told Europe 1 radio.

Agents from France's DCRI domestic intelligence agency working with anti-terror and elite police units carried out the dawn raids in Toulouse, Nantes, Marseille, Lyon, Nice, Paris and other areas.

A policeman searches a house in Coueron, western France, on Friday as part of dawn raids in several French cities. [Photo/Agencies]