A noose was found hanging from a tree outside the Hirshhorn Museum around 6:30 p.m. Friday evening, a spokeswoman said.

The museum had been closed for about an hour when a security guard discovered the noose — historically a racist symbol — and called the U.S. Park Police.

“The Smithsonian is committed to be a welcoming, inclusive, and safe place for all,” Smithsonian Secretary David J. Skorton wrote in an email to his staff. “I know you join me in deploring this act.”

Skorton noted that “a criminal investigation is underway.” A Park Police spokeswoman did not return a request for comment.

Anyone with information about the incident has been asked to call the police at (202) 610-8737.