"The issue has now been resolved and no customer will be left out of pocket as result of this".
The bank's mobile app can not establish a connection, and refers users to an online status page, which fails to open.
Meanwhile, HSBC is carrying out routine essential maintenance this Sunday which means its mobile banking app and online banking will be unavailable for personal customers for a period in the early hours of Sunday morning.
Barclays said it has since fixed the issue.
It comes after City A.M. yesterday reported that Barclays faces a Treasury Select Committee investigation into a failure that saw customers unable to use its online banking services for six hours earlier this week.
It said in a statement: "We would like to apologise to customers who experienced issues logging into their online and mobile banking accounts this morning, this issue has now being resolved". "Sorry and thanks for your patience".
The problem was initially thought to be a glitch affecting only NatWest customers, but it later emerged that there were issues across the RBS banking group.
Why is Natwest online banking down? .
They are still replying with the same message to anyone asking for a status update.
"We're still working through what the issue is".
There is now no firm date as to when the service will be back up and running.
According to NatWest, you can still access your account on the telephone and on ATMs.
How can I access my account?"You can use our automated phone service for transfers, balances and statements".
It has not yet been revealed why the service has gone down.