AT&T says customers facing 'interoperability issue' impacting ability to call non-AT&T users has been resolved

AT&T has resolved the "interoperability issue between carriers" customers were experiencing on Tuesday, the company said in a statement.

Customers began reporting a "nationwide issue that is affecting" their ability to call non-AT&T users, AT&T said at the time.

The company later clarified the network "did not experience a nationwide outage," but some users across the country were affected.

"The carriers are working as quickly as possible to diagnose and resolve the issue," AT&T said.

The company later said that it erroneously sent out a "wireless impact notification" to 911 call centers during the outage.

"Nationwide 9-1-1 Services are operating normally at this time and our customers are not affected," AT&T said in a statement around 5:20 p.m. ET.

The Federal Communications Commission said in a post on X that it was "aware of reports that consumers in multiple states are unable to make wireless calls and we are currently investigating."

Verizon said its network is working normally but some of its users, mostly in the Northeast and Midwest, "are experiencing issues when calling or texting with customers served by another carrier."

This is the second time in three months that AT&T has expereinced an outage.

In late February, AT&T customers across the country experienced a similar outage following a a software update, according to the company.

The February outage temporarily affected 911 services in several states.

The FCC opened an investigation into that incident.

ABC News' Elizabeth Schulze contributed to this report.