Kyoto fire department official Satoshi Fujiwara says 36 others have been injured, some of them critically.
He says firefighters found more than 10 people presumed dead on the top floor of a three-story building, some of them collapsed on the stairs leading to the roof.
Earlier, authorities have confirmed seven dead and six others presumed dead.
A man is suspected of starting the fire early Thursday. He is among those injured in a hospital.
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