Authorities say all schools in Nashua will be closed Monday due to a threat of violence directed toward two schools in the district.

A Nashua Police Department lieutenant says a school administrator received the threat via email on Sunday. That administrator contacted police.

School district Superintendent Mark Conrad said in a statement that students and staff at Nashua High School North and Nashua High School South were threatened with harm.

The police department, school administration and state and federal agencies are working to determine the credibility of the threat.

Conrad says the district is being "cautious" and schools will be closed out of safety.

Lieutenant Kerry Baxter says schools in the district will have extra patrols on Monday.

An investigation is ongoing.