At least four people were wounded in a knife attack on Friday near the former offices of satirical newspaper Charlie Hebdo in Paris.
A Paris police official said that while authorities initially thought two attackers were involved, they now believe it was only one person, who was detained near the Bastille plaza in eastern Paris.
The motive for the attack is unclear, and it is still unclear whether it is linked to Charlie Hebdo, which moved its activities out of the area after Islamic extremists attacked its editorial offices in 2015.
French Prime Minister Jean Castex cut short a visit to a suburb north of Paris to head to the Interior Ministry to follow developments.
The attack comes as a high-profile trial is under way of people accused of helping carry out the attack, in which 12 people were killed.