The fire in a 19-storey building south of Paris was the third fatal blaze in the Paris area in nine days.
The toll rose after a man died late on Sunday in a hospital, where seven others were being treated for serious injuries, police said.
Three teenagers taken in for questioning on Sunday confessed to having started the fire, police said on Monday. Two of the suspects were 18-years-old, the other was 16.
Further details were not immediately available.
Witnesses said they saw a group of youths who lived in the building start the fire, said Patrick Seve, mayor of the town of L'Hay-les-Roses, near Orly airport, where the building is located.
The fire is believed to have broken out in the lobby of the building before raging up a stairwell at least three floors.
Some residents jumped from windows as the blaze flared through the building's entrance.
In response to recent fires, the government announced plans to quickly build more low-income apartments, requisitioning some land to do so.
Interior Minister Nicolas Sarkozy ordered buildings considered dangerous evacuated - a process that began last week.