Three people died and 13 were injured after a blaze broke out in a seven-storey building housing squatters in the Paris suburb of Aubervilliers.
The fire started late Saturday on the third floor of the building, forcing several people to jump out their windows in an attempt to escape the flames.
One person died after jumping and another burned to death on the third floor. The third died in hospital.
Four of the injured were in a serious condition, according to officials.
The cause of the fire was not immediately known.
A resident told journalists the blaze had broken out when someone threw a petrol bomb during a brawl between occupants but that account could not immediately be confirmed.
Housing Minister Cecile Duflot, who travelled to the scene, said authorities had not been aware of any "particular warning signs" at the 1920s-era building.
But Evelyne Yonnet, deputy mayor for housing in the suburb north of the French capital, said the building was "very badly managed" and had been inhabited by squatters.
"There had been complaints from residents," she told journalists.
Resident Ali Belmadi said the building had become "uninhabitable".
"The situation had been getting worse for five years," since squatters arrived, he told AFP.
"There were rats, cockroaches, no security," said another resident named Ghalia.