Two infants died Thursday in an apartment fire in Sapporo, police said.

The brothers, Hibiki Kimura, 2, and Ibuki Kimura, 3, were taken to a hospital, where they were pronounced dead, the police said. Their mother, Ruka Kimura, 22, was treated for smoke inhalation.

The blaze broke out at around 9:35 a.m. on the first floor of their two-story wooden apartment in a residential part of Atsubetsu Ward, the police said.

A room that contained an oil stove was gutted. The mother said the air was thick with smoke when she woke up, according to police and other sources.

The brothers, found in their room, likely died from carbon monoxide poisoning, they said.

A 45-year-old woman who lives in the same building said, "I heard a woman saying her children were inside following a fire alarm . . . I could not see anything because of white smoke when I tried to get out."

"A woman who appeared to be the mother of the boys was trying to break the window with a baby buggy," a 71-year-old man said.