School authorities were warned three years ago about the substandard concrete wall that collapsed onto a 9-year-old girl and killed her following Monday's earthquake in the Osaka area, the local education board said.

In a related development Friday, the local education board in quake-hit Takatsuki, Osaka Prefecture, also said it had discovered another 15 public schools where substandard concrete walls on their premises could pose a danger to students in the event of powerful earthquakes.

According to the board, disaster prevention adviser Ryoichi Yoshida informed them and the school in 2015 about the danger of the high wall, which was made from concrete blocks, around the swimming pool of Juei Elementary School in Takatsuki.