The man’s arrest in Seine-Saint-Denis to the capital’s northeast had previously been reported by broadcaster BFMTV.

Nice chief prosecutor Damien Martinelli confirmed “an arrest” without giving further details, ahead of a press conference later Monday.

One person linked to the three suspects, whose faces were captured on surveillance video, had already been arrested on Friday.

The fire on the top floor of a seven-storey building overnight on July 17th to 18th killed seven people in a single apartment.

Among the victims were three children aged five, seven and 10, a 17-year-old boy, two women aged 22 and 46, and a 45-year-old man who hurled himself from a window to escape the flames.

A 23-year-old man was severely wounded after also jumping, while youths aged 17 and 19 were rescued by firefighters alongside people from neighbouring flats.

Investigators found traces of fires being started on the first, second and third floors, while surveillance footage showed three men breaking into the front door after arriving by car.

They left the building just before the fire was reported, prosecutors said Thursday.

Investigators have urged people to avoid speculating about possible motives for the apparent arson.

But they are probing whether it could be “linked to conflict around the drug trade”.

The Moulins neighbourhood where the apartment block stands is plagued by dealing and repeated violence for control of strategic spots.