Citigroup Inc. said Friday it resolved a technical issue that had left customers unable to access their accounts remotely.

Customers had taken to social media to complain about the outage, which affected several U.S. states, including New York, Pennsylvania and California, according to Bloomberg.

"We experienced a brief technical issue that is now resolved," Citigroup's customer service Twitter account said in response.

Bloomberg reported the news of the outage first.

A Bloomberg reporter spoke with four people in New York City, at a bank branch in the Upper East Side neighborhood of Manhattan, who said debit cards did not work at the ATM there.

Citigroup was not immediately available for further comment.

The bank's shares had closed down 9.4 percent at $40.30 on Friday, as Britain's vote to exit the European Union sparked the biggest global financial shock since the 2008 crisis.