AT&T network services have returned, after a lengthy outage that impacted a large subset of users across North America this week.

The company said in a statement: "Based on our initial review, we believe that today’s outage was caused by the application and execution of an incorrect process used as we were expanding our network, not a cyberattack."

AT&T added: "We are continuing our assessment of today’s outage to ensure we keep delivering the service that our customers deserve."

The outage began around 3:30am Eastern on 22 February and brought down a significant number of AT&T customers. The full scale of the issue is not known, with IBM's X-Force confirming at least 70,000 were disconnected, but others suggesting the number was much higher.

The outage also impacted 911 emergency phone systems in several regions, as AT&T's FirstNet first responders system was brought down.

FirstNet came back around 10.30am Eastern.

AT&T said that it “sincerely apologizes" to customers caught up in the outage.