"We're now experiencing some technical problems - customers are still able to use Barclays Mobile Banking app to check their balance, make and receive payments", the company added.
Barclays said it has fixed problems which saw customers struggling to log in to their accounts and get through on the phone for much of the day on Thursday.
The bank reported that online and telephone operations went down at 10am.
By 5.30 pm, Barclays' website suggested online and mobile banking was back to normal.
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.
Paul Girling told the BBC: "A significant payment due into my account has gone missing".
Customers had been able to use the mobile phone app, although some mobile banking features had also been affected.
The problem comes just months after a prolonged period of IT troubles left TSB customers locked out of their bank accounts.
Customers hit out at the banks on Twitter, with one saying: "Natwest app down again".
Meanwhile Julia from London told the BBC: "The systems have also gone down inside branches with no transactions possible".
The problems have prompted Nicky Morgan, chair of the Treasury Committee, to ask Richard Wagner, chief executive officer of Cashplus, for an explanation and what compensation he is paying victims of the outage.
Update 17:13: Barclays has confirmed the earlier issues have now been resolved, although telephone calls are still subject to lengthy wait times.