The DCRI domestic intelligence service, supported by elite police commandos, carried out arrests in the southern cities of Marseille and Valence, two towns in the south-west and in the north-eastern town of Roubaix, a police source said.
The pre-dawn raids follow the arrest of 19 people on 30 March, a week after police snipers shot dead Mohamed Merah, who killed three Jewish schoolchildren, a rabbi and three soldiers in a spate of attacks around Toulouse.
"Those arrested have a similar profile to Mohamed Merah," a local police source said. "They are isolated individuals, who are self-radicalised."
He said the suspects were tracked on Islamist forums expressing extreme views and said they were preparing to travel to areas including Afghanistan, Pakistan and the Sahel belt to wage jihad.
Some of those arrested had already travelled and returned to France, the source said.
Sarkozy, who is facing an uphill task to be re-elected, has vowed to root out militancy following the Toulouse killings.
Thirteen of the 19 people arrested last Friday are alleged to have links to radical French Islamist group Forsane Alizza. They are being investigated on suspicion of terrorism, the Paris public prosecutor said on Tuesday.
Wednesday's raids were not linked to either those arrests or the Merah attacks, the source said.
The Toulouse killings have pushed domestic security up the political agenda before the 22 April first-round vote and may have improved Sarkozy's chances against his Socialist rival, François Hollande.
Sarkozy, a former interior minister, has been accused by opponents of capitalising on the Islamist threat for electoral purposes even though only polls show only 20% of voters consider it their main concern.
Speaking on RTL radio, Hollande declined to be drawn on whether he thought the raids were politically driven.
"If there are suspicions and risks, then they must be acted upon," he said. "But why do it after a terrorist act? I am not questioning what is being done, but we could have done more before," he said.
