Minneapolis Police Sgt. Jesse Garcia says officers learned early Wednesday that someone had threatened to open fire in a school then shoot themselves.
The threat was made on two social networking sites. He says the threat didn't specify which school was the target, so the district decided to lock down all its buildings.
Garcia says at a news conference that police are taking the threats seriously and working to track down who posted them.
District spokeswoman Emily Lowther says the 34,000 students in the district continue to go to class, but access to the buildings is restricted. She says parents have been notified of the situation.
It's likely that the alert status will last for the remainder of the day. The district notified parents with its automated telephone system. Another announcement will go out when the district knows more.