US carrier Verizon has confirmed that last week's network outage was caused by a software issue.

The telco suffered a nationwide outage last Wednesday (January 14).

"This was a software issue, and we are conducting a full review of what happened. As of now, there is no indication that this was a cybersecurity issue,” said Verizon officials in a statement.

Verizon's outage impacted thousands of users, with many reporting that iPhones were stuck in 'SOS Mode.'

The outage was fixed within 12 hours, according to data from Downdetector, which reported a total of 2.3 million reports of users being impacted by the outage.

Verizon didn't give the cause of the outage at the time, noting that it was working to restore services.

A day after the outage, the carrier said it was issuing $20 account credit to users as a gesture of goodwill, while the company apologized for the outage.