THE problems were first reported at 5.30am this morning (Thursday)
O2 customers across Newry, Mourne and Down have reported problems using data and 4G services.
The issues were first reported at 5.30am today (Thursday) by users on Twitter who said they could not access the internet without using their WiFi connection.
An O2 spokesperson confirmed the problems, saying: "Our technical teams are investigating reports of issues when using data.
"Voice calls are working OK. We apologise for any inconvenience."
O2, with 25 million direct customers, is the second-largest mobile network in the country, behind EE, however it also provides services for the Sky, Tesco, Giffgaff and Lycamobile networks.
That brings the total number of people affected up to 32 million.
UPDATE: A spokesperson for O2 said in a further statement: "We’re aware that our customers are unable to use data this morning.
"One of our third party suppliers has identified a global software issue in their system which has impacted us. We believe other mobile operators around the world are also affected.
"Our technical teams are working with their teams to ensure this is fixed as quickly as possible. We’d encourage our customers to use Wifi wherever they can and we apologise for the inconvenience caused."