North Atlanta High School went into a "hard" lockdown after receiving an anonymous threat, Principal Angela Mitchell said in a message to parents. Atlanta police officers and K-9 units were sweeping the campus.

Mitchell asked parents not to come to the school and not to call students or the front office, saying phone lines and quiet inside classrooms must remain open for safety protocols. All students, faculty and staff were secured inside classrooms and designated safe areas, with exterior and interior doors locked and no one permitted to enter or exit the building, according to the letter.

Carver High School, roughly 13 miles south of North Atlanta High, was also locked down "due to security concerns in the surrounding community," Atlanta Public Schools said. The district confirmed the lockdown was linked to a separate police situation but did not specify what those concerns were.

Marist School, a Catholic private school serving grades 7 through 12 near Brookhaven, said it was on lockdown due to a threatening phone call. The campus was blocked off, and parents were asked not to come.

The lockdowns come as schools across the metro area continue to grapple with how to respond to threats, which can disrupt instruction and unsettle families even when no danger is confirmed. District officials have emphasized in past incidents that locking down buildings and limiting phone traffic are standard precautions meant to keep students safe while law enforcement assesses a threat.

It was not immediately clear whether the three lockdowns were connected. No injuries were reported, and authorities had not announced any arrests or charges as of Wednesday afternoon.

This is a developing story. Check back for updates as more information becomes available.