BATTLE GROUND, Wash. (AP) -- Six schools in suburban Vancouver were closed and nearly 4,300 students were told to stay home Wednesday after multiple threats made against students and staff at one of the schools were found to be credible, authorities said.

The written threats were made Tuesday against Chief Umtuch Middle School in the city of Battle Ground, school district spokesman Gregg Herrington said.

That school was closed, along with four others on the same campus - Captain Strong Primary, Summit View Middle School, CAM Academy and Battle Ground High School. A nearby private school also stayed closed for the day as a precaution.

Police Lt. Roy Butler said officers inspected the five public schools, and nothing suspicious was found.

He said police are not releasing details of the threats as they continue their investigation, but they determined the threats were not a prank. Investigators are consulting with the FBI.