French police have arrested a man suspected of starting a fire that killed eight people, including two children, in northern Paris.
The apartment block blaze in the 18th district of the French capital broke out in the early hours of Wednesday, and took more than 100 firefighters to contain it.
Four survivors - some of whom are in a critical condition - are in hospital.
A police source said the suspect was found with "a candle and lighter".
The French website TF1 adds that the man in his 30s was already known to the police.
Police sources say that the arrest was made on the basis of eyewitness testimony and CCTV footage.
The cause of the fire in the building at 4 rue Myrha, located at the foot of the famed Montmartre hill, is being investigated by criminal prosecutors.
Interior Minister Bernard Cazeneuve told Europe 1 radio that the investigators were "focusing on the possibility of criminal intent".
Fire crews were first called to the scene at about 02:20 local time (00:20 GMT) and quickly put out the blaze, but they were then called back again two hours later to extinguish a second, much larger fire.
"It's clear that when you have two call-outs in the same night... this could be a malicious act," interior ministry spokesman Pierre-Henry Brandet said.
The larger blaze is believed to have started on the ground floor before quickly spreading into the stairwell and then upper floors.
Some of the residents reportedly attempted to escape through windows.
The fire broke out in a private building, not a block of flats for low-income families, Paris Mayor Anne Hidalgo said.
She added that about 15 other buildings in the area had been affected by the blaze.
This is believed to be one of the deadliest fires in the French capital in the last decade.
In a statement, French President Francois Hollande said: "Everything is being done to shed light on the cause of this tragedy."