A French prosecutor said Thursday he would pursue charges of attempted murder and terrorism against seven of the 12 suspected Islamist extremists arrested at the weekend.

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François Molins, the Paris prosecutor, said the seven had been part of an "active terrorist cell" that posed the biggest threat of its kind that France has faced since the mid-nineties, when the Algerian-based GIA was dismantled.

The attempted murder charges relate to a grenade attack on a Jewish grocery store in the Paris suburbs last month.

The attack left one person slightly injured but Molins said the Yugoslav-made grenade had been capable of seriously injuring anyone within a ten-metre radius, indicating the consequences could easily have been much worse.

The prosecutor added that the profile of the suspects detained in custody was "much more dangerous than we initially assumed" and said the investigation had uncovered evidence they were planning to go on 'jihad' in Syria and other countries.

The grenade attack on a kosher grocery in Sarcelles, just outside Paris, triggered an investigation which led to Saturday's arrests.

One alleged leading member of the group, 33-year-old Jérémie Louis-Sidney, was shot dead after he opened fire on officers seeking to arrest him in a dawn raid at his home in Strasbourg.

Police have since discovered weapons and significant amounts of bomb-making equipment at the homes of some of the other men detained under anti-terrorism legislation.

Five of the 12 initially detained were released without charge on Thursday. 

The other seven are all French citizens, aged between 19 and 25, Molins said.