A Barclays spokesperson said: "We're very sorry about the technical problems our customers have experienced today".
Barclays customers across the North West would have received a message this morning when attempting to access services saying: "Sorry - Barclays Online Banking is now unavailable".
The banking giant was inundated with hundreds of complaints from angry customers on social media as people found they were unable to access their accounts. "Everything is now back up and running, and we're really grateful for customers bearing with us".
But one alarmed customer said money had disappeared from his account.
United Kingdom bank customers have faced more misery as Royal Bank of Scotland became the latest lender to suffer problems with its mobile banking services, leaving millions without online access to their accounts. "It has been confirmed as sent but not received".
The service status report on the Barclays website confirms there is an outage of both online and telephone banking.
Several killed as gunmen attack military parade in Iran
Early reports Saturday described the assailants as "Takifiri gunmen", a term previously used to describe the Islamic State group. The Guards also play a major role in Iran's regional interests in countries such as Iraq, Syria and Yemen.
A number of business customers have complained that they are now unable to organise tomorrow's payments for staff.
The bank emphasised that it was an "access issue" and there is no evidence that customer data was compromised.
The problem comes just months after a prolonged period of IT troubles left TSB customers locked out of their bank accounts.
A statement published to Twitter advised customers to use the mobile app to access their accounts.
Another customer told the BBC that: "The systems have also gone down inside branches with no transactions possible".