Thousands of O2 customers in Northern Ireland have been left without data on Thursday morning due to a technical issue.
Customers have reported being unable to access the internet and other services across the network.
The company has 25 million customers across the United Kingdom.
An additional seven million customers of Sky, Tesco, Giffgaff, and Lycamobile, which O2 provides services for, are also impacted.
The first issues were reported at around 5.30am on Thursday.
A spokesperson from the network has said it is investigating a technical fault that has left thousands of mobile customers unable to get online.
It has confirmed engineers are working to fix the issue.
"We are aware our customers are unable to use data this morning," the company said on its official Twitter account.
"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."
The service status page of the O2 website added that "voice calls are working OK" and apologised for any inconvenience caused.
O2 said it would share further updates as soon as they were available.
In a further tweet, O2 said the problem was related to a software issue in the system of a third party supplier.
"One of our 3rd party suppliers has identified a software issue in their system. Our technical teams are working extremely hard to resolve this," the company said.
"We'd encourage you to use Wi-Fi wherever you can and we are really sorry."