Target acknowledged nationwide “system issues” affecting its stores on Saturday that prevented its customers from checking out at registers. The outage caused long checkout lines at Target locations, with upset customers posting images and video on social media. It’s unclear what caused the outages.

In a statement to CBS News, the company said, “We’re aware that guests are currently unable to make purchases at Target stores. Our teams are troubleshooting now and we apologize for the inconvenience.”

Target, which has more than 1,800 stores across the U.S., said it would “provide an update as soon as possible.”

© 2019 CBS Interactive Inc. All Rights Reserved.