An American flag at the U.S. Post Office in Port Washington was mysteriously replaced with a Russian flag at some point between Sunday afternoon and Monday morning, authorities say.

An employee at the post office, located at 1051 Port Washington Boulevard, noticed what appeared to be a Russian flag hanging from the mast on Monday morning, according to Port Washington Police Chief James Salerno. The postmaster immediately notified the Postal Inspection Service and the local police, the U.S. Postal Service said.

"We in the Postal Service appreciate the seriousness of this apparent act of vandalism and we share the concerns of the community of Port Washington regarding this recent incident involving our flag," a USPS communications representative told Patch in an email. The incident is being investigated by the U.S. Postal Police.

"We are proud to display the American flag today, tomorrow and every day outside our offices," USPS said in a statement. Several residents in a community Facebook group suspect that the tampering was a prank done by seniors at Paul D. Schreiber High School. The post office is located a short distance away from the high school. Last year, several high school students released chickens onto the school track as part of a senior prank.

Patch reached out to the U.S. Postal Service and Port Washington Police to see if they had a picture of the incident. They did not. If you or anyone have a picture of the flag tampering or any additional information on the incident, please email paige.mcatee@patch.com. Names will be kept anonymous at your request.