Police have opened an investigation into the group that organized a mountaineering lesson during which seven high school students and a teacher were killed by an avalanche at a ski resort in Tochigi Prefecture, investigators said Tuesday.

The police will assess whether sufficient steps were taken to ensure the safety of the students taking part in the program.

Although the lesson originally was intended to teach mountain climbing, it was changed to deep snow traversing due to weather conditions at the site by teachers on location. Tochigi Prefecture's high school athletic federation was unaware of the change, a senior official of the organization said.