PARIS (Reuters) - French anti-terrorist police have found bomb-making materials and weapons while investigating suspected radical Islamists across the country, Paris prosecutor Francois Molins said on Wednesday.

Molins said a dozen suspects rounded up in raids over the weekend would be held for a further 24 hours after the discovery of chemicals used to make explosives at a garage in the Paris suburbs belonging to one of them.

"We are clearly confronted with an extremely dangerous terror network," Molins said in a statement to the media. "It is essential to extend their stay in custody."

Investigators searched garages in the town of Torcy, near Paris, overnight after an anti-terrorist raid on Saturday ended with police shooting dead an Islamist suspect linked to a grenade attack last month on a Jewish supermarket and arresting 11 others.

Molins said a shotgun, a revolver, bags of potassium nitrate, sulfur and a pressure cooker were discovered at a garage used by the suspect, at whose home police on Saturday had found a list of Jewish groups in the Paris area.

"These are all products used to make what we call improvised explosives," he said.

France's Jewish community has been on edge after a series of attacks in recent months. In the worst incident, three Jewish children and a rabbi were among seven shot dead in the southern city of Toulouse in March by an al-Qaeda-inspired gunman.

Last week, the government said the terrorist threat remained high as it presented legislation allowing police to arrest those believed to have been involved in terrorism-related activity outside French borders.

Molins said the detention of the dozen suspects could be extended again by a further six days if necessary.

(Reporting by Catherine Bremer; editing by Mark John)