PHOENIX (AP) - Authorities say a 16-year-old girl from Mesa was arrested Thursday after she posted a threat on YouTube that she planned to kill people at her high school and then commit suicide.

The Maricopa County Sheriff Office says the girl had access to guns at her home, but never brought firearms to Red Mountain High School in Mesa.

The agency says investigators arrested the girl at her home Thursday morning and that she admitted to posting the threat.

The school was in session Thursday.

Investigators say they received a tip late Wednesday night from Canadian police who were alerted of the posting by the group that set up the YouTube channel where the posting was made.

The girl was booked on suspicion of computer tampering and of intimidation and making threats.