PARIS  - French police arrested 19 people in a crackdown on suspected Islamist networks Friday as President Nicolas Sarkozy made the battle against extremism the keynote of his re-election campaign.

Arrests took place in several cities, including Toulouse, where extremist gunman Mohamed 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.

Agents from the DCRI domestic intelligence agency and elite police carried out the dawn raids in Toulouse in the southwest, the Paris region, Nantes in the west, Lyon in the southeast and the Provence region.

Three of the 19 suspects arrested were women, police said.

Judicial sources said 17 of those arrested were being held for questioning. In France, suspects in terror-related cases can be held for up to four days without charge.

A senior police source told AFP authorities had up to 100 suspected Islamist radicals in their sights and Sarkozy said Friday's operation was only a start.

"There will be other operations that will continue and will also allow us to expel from our national territory a certain number of people," said Sarkozy, in the thick of campaigning for France's April-May presidential election.

"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.

After trailing Socialist candidate Francois Hollande for months in the polls, Sarkozy has jumped ahead in first-round voter intentions and seen his support rise in the wake of the attacks.

Generally seen as stronger on security than Hollande, Sarkozy is keen to make law and order a key issue in a campaign that has so far been dominated by the economy, jobs and spending power, where the Socialist is stronger.

The latest poll by CSA released Wednesday said 30 percent of voters would pick Sarkozy and 26 percent would go for Hollande in the April 22 first round. But all polls still predict Hollande winning the May 6 second round.

Sarkozy said Friday's raids were not directly linked to the Toulouse shootings but targeted at extremists networks. Police said Kalashnikov assault rifles and other weapons were seized.

Among those arrested in the Nantes region was Mohammed Achamlane, the head of a suspected extremist group called Forsane Alizza, the sources said. Three Kalashnikovs, a Glock pistol and a grenade were seized from his home.

Some of Sarkozy's opponents branded the arrests a public relations stunt, with Steeve Briois, the general secretary of the far-right National Front, calling the raids "an electoral manoeuvre".

"The 'big haul' made overnight by the DCRI and the RAID - the elite police unit that shot Merah - doesn't fool anyone," he said in a statement.

"Waiting for the horror of the Toulouse killings to start taking action shows the cynicism and opportunism of Nicolas Sarkozy."

But Interior Minister Claude Gueant said there was no reason beyond security for the arrests.

"These are people who on the web... claimed support for a radical extremist ideology, for an ideology of combat," he told journalists.

The arrests came a day after the body of Merah, who was shot dead by a RAID sniper on March 22 at the end of a 32-hour siege at his flat in Toulouse, was buried in the city under heavy police guard.

The 23-year-old had shot dead three soldiers, and three children and a teacher at a Jewish school, in a killing spree this month that shocked the country.

On Thursday, France banned four Muslim preachers from entering the country for a conference of the Union of Islamic Organisations in France (UOIF), saying their "calls for hatred and violence" were a threat to public order.

The ban applies to Saudi clerics Ayed Bin Abdallah al-Qarni and Abdallah Basfar, Egyptian cleric Safwat al-Hijazi and a former mufti of Jerusalem Akrama Sabri, who had been due in Paris next month.

National Front presidential candidate Marine Le Pen on Friday called for the conference to be cancelled and the UOIF to be disbanded.

"Drastic measures must be taken without delay and without weakness against ‘radical’ Islam," she said in a statement, describing the group as "close to Islamists, if not even terrorists."

Interior Minister Gueant and Defence Minister Gerard Longuet meanwhile rejected a call for the heads of France's intelligence agencies to appear before a commission in the Socialist-controlled upper house of parliament to answer questions about the Merah murders.