O2 customers have lost access to services this morning.
The mobile phone company said it is aware that customers are unable to use data this morning and are working to resolve the issue.
O2 said that a "software issue" has been identified.
O2 said: "Our teams are working closely with one of our third party suppliers who has identified an issue in their system which has impacted mobile services globally.
"This is our top priority and we are really sorry.
"Our technical teams are working extremely hard to resolve this. We'd encourage you to use Wi-Fi wherever you can and we are really sorry."
An earlier statement had read: "We are aware our customers are unable to use data this morning. Our technical teams are working on the issue with high priority. We are really sorry and working as hard and as fast as we can to fix this."
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