The Egyptian man was arrested a week ago in the French capital's 18th arrondissement, or district, according to a security official. Authorities found explosive powder and tutorials on how to make explosives and poison from materials such as ricin, the official said.
The man, identified as Mohamed M., was handed preliminary charges of association with a terrorist enterprise, according to a judicial official. Another man was also arrested but later released. A police official said both men were born in 1998 and at least one was a college student.
The officials weren't authorized to be publicly named discussing the investigation. Earlier, Interior Minister Gerard Collomb said the two men arrested were brothers. But the other officials said later they weren't brothers. The reason for the discrepancy wasn't immediately clear.
Authorities were tracking extremist activity on social networks when they identified the two young men, Collomb said earlier on BFM television. Collomb said the men had been communicating on encrypted messaging app Telegram.
"We were able to detect them, detect this attack plan and were able to arrest them," he said. He also defended the government's handling of the 26,000 people on police watch lists for suspected radicalism. The assailant in Saturday's stabbing, a 20-year-old Frenchman of Chechen origin, had been on the watch list, like several others who have attacked France in recent years.
Assailant Khamzat Azimov, a nursing student, killed one person and wounded others in the attack near the Garnier Opera house. Azimov was killed when he advanced on police. A close friend of his was arrested and given preliminary terrorism charges Thursday night. Two female friends of the men were arrested Thursday in the Paris region, the anti-terrorism prosecutor said.
The Islamic State group claimed responsibility for inspiring Azimov's attack. IS sympathizers have killed more than 200 people in France in recent years.