According to Down Detector, which monitors website outages, some 2,000 users began experiencing issues at around 06:00 BST.
Barclays confirmed the issue had been fixed shortly after 09:00 BST but did not elaborate on the cause of it. Neither did HSBC and NatWest when they both suffered online banking problems on Monday.
A Barclays spokesman told MailOnline: ‘We apologise to customers who have been unable to access the Barclays app, and can confirm the service has been restored.
‘Our online banking and automated telephone service were not impacted and customers were able to transfer funds, make payments and check balances.’
Barclays’ mobile banking app is back up and running after a three-hour outage that saw thousands of customers unable to access their accounts
According to Down Detector, which monitors website outages, some 2,000 users began experiencing issues at around 06:00 BST
A number of people had taken to social media to express their frustration over the outage.
One Barclays customer wrote on Twitter: ‘Barclays is there a problem with online banking can’t see my account??’
Another added: ‘Is anyone else’s Barclays app down?? Can’t see any of my accounts when I open the app?’
The majority of issues reported – 68 per cent – related to mobile banking, while a further 25 per cent were about online banking and 7 per cent mobile log ins, according to Down Detector.
On Twitter, the bank acknowledged it was having problems, writing: ‘We’re looking into the problem now, and we’ll update you here as soon as possible.’
Replying to one customer, Barclays UK Help tweeted: ‘Thanks for your message and please don’t worry! We’re aware of the issues with the app, the team are working hard to fix this ASAP.’
A number of people took to social media to express their frustration about the outage
Down Detector’s ‘heat map’ of user-submitted problem reports showed that affected customers were mostly in London and Plymouth
Down Detector gets network status updates from various sources including social media and reports submitted to its website.
The website’s ‘heat map’ of user-submitted problem reports showed that affected customers were mostly in London and Plymouth, with other cities such as Manchester, Birmingham and Nottingham hit too.
The outage came just 48 hours after both HSBC and NatWest also suffered problems with their online banking systems.
On Monday morning, HSBC customers were unable to access their accounts for around two hours before the problem affecting HSBCnet was resolved.
A few hours later NatWest also experienced issues, with its customers struggling to log into their accounts via online and mobile banking.
Both banks apologised for the disruption when the problems were fixed but neither revealed the cause of their respective outage.