Kansas-based Fidelity Bank has revealed that a failure in a "key piece of hardware" impacted the organisation's online and mobile banking systems.
Customers in Wichita and Oklahoma were affected by the downtime and Al Sanchez, spokesman for the bank, said he hoped the outage will be fixed and fully restored in the very near future.
The bank stressed that the mobile and online banking downtime was not caused by a cyber attack or a breach of its security systems.
Mr Sanchez added: "No loss of data has occurred and no confidential information was at risk."
All transactions are being recorded and Fidelity has said that customers needing to make transactions before the systems are restored and running correctly can visit a branch or call its customer service department.
Telephone banking had been impacted by the hardware issues, however customers were still able to withdraw cash from automated teller machines (ATMs) as usual.
By Tony Aynsley