Paris (CNN) -- Police who searched buildings in Paris as part of a far-reaching investigation into a suspected terrorist cell found "all the elements needed for making explosives," prosecutors said Wednesday.
The searches were connected to a big police operation Saturday targeting radical Islamists suspected of involvement with the bombing of a Jewish supermarket in September.
Paris prosecutor Francois Molins said Wednesday that the 12 suspects in custody would be detained for an additional 24 hours. Normally French authorities can only hold suspects for 96 hours before they must press charges or release them.
Police who searched premises in Torcy, about 25 kilometers (16 miles) east of Paris, overnight Tuesday found bags of potassium nitrate, sulfur, saltpeter, pressure cookers and headlight bulbs, all items useful in making homemade explosives, Molins said in a statement.
A shotgun and handgun were also found, he said. The search continued Wednesday morning.
The premises where the alleged explosives components were found are used by the same person at whose address a list of Jewish organizations was found by police Saturday, Molins said.
However, police inquiries suggest that two people suspected of throwing a grenade through the window of the Jewish supermarket in Sarcelles, a Paris suburb, may still be at large, he said.
Given the nature of the discoveries made by police and the need to find all the members of the presumed terror cell, it was vital to extend the detention of the suspects by an additional 24 hours, Molins said.
This step is allowed under French law if there is a serious risk of an imminent terrorist threat, and can be renewed once, leading to a maximum possible period of detention without charge of six days. It is only the second time this provision has been used since it came into law in 2006, he said.
"We are clearly and objectively facing a terrorist cell of an extreme dangerousness," Molins said.
Authorities will do everything in their power to put an end to the cell's actions and avoid any risk of a terrorist attack in France, he said.
The suspects are being held on suspicion of having links to terrorism, manufacturing deadly explosives, illegal possession of weapons and attempted homicide of police officers.
Three of them have criminal records for drug trafficking, theft or violence, Molins told reporters Saturday. One man who was arrested on top of a building in Torcy on Saturday was armed with a loaded .22-caliber pistol, Molins said.
The chief suspect in the September bombing, 33-year-old Jeremie Louis-Sidney, died in Saturday's operation as he traded gunfire with police in a Strasbourg apartment building.
French intelligence operatives had been monitoring him since spring -- well before the Sarcelles attack -- but he had not been questioned by authorities, Molins said.
He was sentenced to two years in prison in 2008 after being convicted of drug trafficking. "He appeared (to be) a delinquent converted to radical Islam," Molins said.
Police seized items such as ammunition, a list of "Israelite" organizations in and around Paris, a publication produced by al Qaeda in the Arabian Peninsula, wills, computer equipment and 27,000 euros ($35,000) in cash, the prosecutor added.