Police on Wednesday took a 17-year-old man into custody for being in contact with the assailant who killed three people in a knife attack on a church in the French city of Nice, a judicial source said.
The young man is believed to have been in online contact with the Tunisian assailant, Brahim Issaoui.
Four other people, arrested Tuesday, were still in custody late Wednesday.
But a 29-year-old Tunisian, arrested on Saturday, was released on Wednesday without charges.
Issaoui, 21, remains hospitalised after being shot several times by police following the knife rampage at Nice's Notre-Dame basilica on Thursday.
He has since tested positive for COVID-19, which could further delay his questioning, a source close to the case said.
In the attack, one woman had her throat cut and a church employee was also fatally stabbed inside the church, while another woman managed to flee but later died of her wounds.
Police say Issaoui yelled "Allahu Akbar" (God is Greatest) as they apprehended him, leading officials to say it was the latest in a string of attacks labelled as "jihadist attacks" on French soil in recent years.