GRAND FORKS, N.D. (AP) — The lockdown has been lifted at Grand Forks Air Force Base in North Dakota after a report of a gunshot on Wednesday afternoon sent people indoors.

Security officers completed a door-to-door sweep but did not locate a source of the sound, the base said in a social media post. No injuries were reported.

The base said in an earlier post that security at the base received the report of a single gunshot near the medical clinic and base exchange around 1 p.m. The lockdown was ordered “out of an abundance of caution,” the statement said. The lockdown lifted about 3 1/2 hours later and “normal operations have resumed,” the base said.

State Sen. Scott Meyer said he was walking out to his vehicle at about 12:45 p.m. after having lunch at the base’s bowling alley, and he saw three or four squad cars with lights on at the commissary.