AT&T's massive outage on Thursday, which left thousands without service for hours, was most likely caused by a procedural error rather than a cyberattack, the carrier said.

The difficulty began early Thursday, but by the afternoon, AT&T stated that all customers' service had been restored.

According to an initial analysis, the company believes the outage "was caused by the application and execution of an incorrect process used as we were expanding our network, not a cyber attack," it stated Thursday evening.

Customers reported more than 32,000 AT&T outages about 4 a.m. ET on Thursday. According to the site, reports decreased before increasing to more over 50,000 about 7 a.m., with the majority of troubles reported in Houston, Chicago, Dallas, Los Angeles, and Atlanta.

That figure jumped to almost 71,000 just before 8 a.m. ET.

AT&T recognised the issue Thursday morning, stating, "Some of our customers are experiencing wireless service interruptions this morning."

Other cellular companies, such as Verizon, T-Mobile, and Cricket Wireless, have also experienced problems. Verizon and T-Mobile said those affected had attempted to contact AT&T customers.

Verizon stated Thursday morning that the outages are not affecting its network directly, but rather users attempting to contact another carrier.

T-Mobile also confirmed early Thursday that there was no network interruption.

Cricket Wireless, which is owned by AT&T and operates on its network, also suffered cellular issues. More than 13,500 subscribers have reported disruptions as of 8 a.m. ET Thursday. By 10 a.m., the number had dropped to roughly 10,000.

"Allow us to explain that there is a nationwide network incident impacting multiple services," the business said in a blog post. "It is Cricket's top priority to restore service to full capacity as quickly and safely as possible."

Service has since been restored to all affected AT&T customers.

"We've restored wireless service to all of our affected clients. We truly apologise to them. "Keeping our customers connected remains our top priority, and we are taking steps to ensure this does not happen again in the future," the business stated in a statement.