The suspect later told police that he had wanted to attack a soldier and had been in touch with a member of the Islamic State group who encouraged him to do so, according to the official close to the investigation.
The official said on Sunday the claim prompted investigators to upgrade the seriousness of the alleged offence, which originally they classified as a common crime by someone with a history of psychiatric problems. As a result, the probe has been handed to counterterrorism prosecutors.
The man is now under investigation for involvement in a terrorist enterprise and an attempted terrorism-related attack on security forces.
The suspect was born in Mauritania in 1998 but has French citizenship, the official said. His name wasn't released.
The Eiffel Tower was lit up on Saturday night in the colours of the Paris-Saint Germain soccer club and with lights welcoming star Brazilian striker Neymar to the team.