Washburn High School in Minneapolis was briefly placed on lockdown Thursday after ammunition was found on campus, school officials said.
School staff responded appropriately and confiscated the ammunition," the school said in an automated call to parents.
No weapons were found, the school said.
Tonya Tennessen, chief communications officer for Minneapolis Public Schools, said the high school was placed on a code yellow.
"This was done out of an abundance of caution while staff confirmed there was no weapon," Tennessen said in a statement. "Maintaining a safe environment for our students and staff is our highest priority."