GRAND FORKS, N.D. (AP) — Security officers were conducting a door-to-door sweep Wednesday at a North Dakota Air Force base after a report of a gunshot prompted a lockdown.

The Grand Forks Air Force Base said in a social media post that security at the base received a report of a single gunshot near the medical clinic and base exchange at around 1 p.m. The lockdown was ordered “out of an abundance of caution,” the statement said.

By mid-afternoon, no injuries were reported and the sweep of the facility was still ongoing.

Grand Forks County Chief Deputy Sheriff Dave Stromberg said the office knows of no active threat on the Air Force base, and that base officials have not asked for assistance.

No one answered the phone at the base’s public affairs number, and there was no immediate response to emails to the public affairs office.

The base’s website says that 2,200 people are assigned to the 319th Reconnaissance Wing. The base houses air and space operations.