The United States Naval Academy in Annapolis, Md., was placed under lockdown on Thursday after receiving threats, a spokesman said.

Local law enforcement officers were responding to the campus, said Lt. Naweed Lemar, a spokesman for the U.S. Navy.

The Annapolis Police Department declined to comment.

A nearby military base, Naval Support Activity Annapolis, which provides security and other support for the academy, was also responding, Lieutenant Lemar said. He did not describe the threats.

According to emails shared with The New York Times, at 5:32 p.m., an academy midshipman who was standing watch sent an email to students warning them to “get inside and lock your door right now. Not a drill. Get inside and lock your door.”

This is a developing story.