Defence Minister Jean-Yves Le Drian said France was deliberating whether its current actions in Iraq are sufficient against IS.
Two minors were among those arrested near Lyon on suspicion of recruiting young women to fight in Syria.
During visit to Baghdad, François Hollande said he underlined France's readiness to provide even more military assistance to Iraq.
Interior minister Bernard Cazeneuve said suspect had 'key role' in recruiting French youths in Strasbourg and Toulouse and sending them to Syria.
Foreign minister calls for international mobilization against militants from Islamic State group whom he described as a 'transnational danger'.
Libération insists Mehdi Nemmouche told journalists held hostage in Syria of his plan to attack Paris, but interior minister dismisses claim.
Journalist Nicolas Henin said Mehdi Nemmouche, who has been extradited to Belgium over murders, was his jailer in Syria in late 2013.
Young Frenchman says jihadists use online method showing shocking images that paint the Western world as degenerate and corrupt.
Meriam Rhaiem, 25, made headlines earlier this year with an emotional appeal to recognise her baby girl, aged 2, as 'the youngest French hostage'.
The pair, aged 15 and 17, were arrested on suspicion of helping a 14 year-old girl travel to Syria to join jihadist forces.
Proposed bill includes ban on foreign travel for individuals suspected of being radicalised, plus powers to confiscate their passports.
The 16-year-old, who is now in police custody in France, headed to Syria to fight after telling his father he was going to a nightclub.
The recent arrest of a French citizen accused of a murderous attack at a Jewish museum in Belgium has highlighted the growing problem of jihadists returning from Syria to wage war in their own countries. More than 2,000 European citizens, including 630 French residents, have gone to fight against the Assad regime since 2011, according to recent figures. And some, at least, of those who return come back intending to use their combat training to carry out terrorists attacks at home. As Louise Fessard reports, the numbers involved are so great that European security forces, including those in France, are struggling to cope.
The four were detained in Marseille over allegations that they have been helping to recruit volunteers for radical Islamist networks in Syria.
French interior minister says Souad Merah, whose brother shot dead seven people in south-west France in 2012, is believed to be in Syria.