The Paris prosecutor's office said it filed preliminary charges against Mr. Sahnouni for "criminal association with the goal of preparing terrorist actions."

Moroccan police said Mr. Sahnouni, born in Casablanca, Morocco, headed a cell of 24 suspected terrorists arrested last month in the North African kingdom, where they were allegedly plotting large terror attacks. In an unusually detailed statement, Morocco's Interior Ministry said the cell planned to murder "symbols of the state" and attack foreign interests in the kingdom, a tourism haven and a strong Western ally in fighting terrorism.

It said several of the cell's members were caught on their way to Somalia where they planned to join an Islamist militia. Others were preparing training camps to support al Qaeda militants in North Africa, Moroccan authorities say.

French counterespionage said Mr. Sahnouni was arrested late Friday in Aubervilliers, a working-class suburb northeast of Paris. Police seized computer material, radical Islamist propaganda and photos of Mr. Sahnouni training with weapons. French justice officials says the suspect admits to having traveled to various Arab countries, but denies heading a terror cell.