By David Shepardson

(Reuters) – AT&T (NYSE:) said late on Tuesday that an issue that had prevented making some calls to other wireless carriers had been resolved.

Earlier, AT&T, Verizon (NYSE:) and T-Mobile said they were all experiencing issues with some calls between carriers.

“The interoperability issue between carriers has been resolved. We collaborated with the other carrier to find a solution and appreciate our customers patience,” AT&T said in a statement.

Some customers in multiple states had said they were unable to complete calls, prompting the Federal Communications Commission to investigate.

Verizon said in a statement earlier that its network was operating normally, but some customers in the U.S. Northeast and Midwest were “experiencing issues when calling or texting customers served by another carrier.”

Tracking website showed more than 2,300 outage reports as of 5:46 p.m. EDT, with the New York City borough of Brooklyn, Chicago and Philadelphia among the most reported locations.

T-Mobile US (NASDAQ:) said it was “not experiencing an outage. We are seeing Down Detector increases with other providers, so this likely could be challenges our customers are having connecting with users on other networks.”

© Reuters. FILE PHOTO: An AT&T logo is pictured in Pasadena, California, U.S., January 24, 2018. REUTERS/Mario Anzuoni/File Photo

The FCC and New York Attorney General Letitia James said in February they were investigating the cause of an AT&T outage that month as well as the telecom firm’s response. The outage lasted more than 10 hours and impacted more than 70,000 customers.

AT&T credited customers a full day of service for the outage.