Verizon reported late Monday afternoon progress in resolving a “network issue” that led to widespread outages in parts of the U.S., including the Chicago area.

In a post on X, the social media platform formerly known as Twitter, at 4:04 p.m., the wireless carrier said its engineers are “making progress on our network issue and service has been restored.”

“We know how much people rely on Verizon and we apologize for any inconvenience some of our customers may have experienced today,” the company continued. “We continue to work around the clock to fully resolve this issue.”

The problem appeared to knock out cell phone service for tens of thousands of Verizon users. Data from the outage tracker DownDetector shows that reports reached the 100,000 mark shortly after 10 a.m. CT — and while that number dropped significantly, nearly 48,000 were still experiencing issues around 3 p.m. CT. In the Chicago area, more than 4,000 customers reported being without service at the height of the outage, around 10:30 a.m. Around 2:30 p.m., the number of reports had dropped to approximately 1,200.

An outage map from Downdetector showed that the “most reported” outage locations were Chicago, Indianapolis, Minneapolis, Phoenix, Omaha, Cincinnati, Denver, Seattle and Columbus.

The Federal Communications Commission, the national agency that regulates interstate and international communications, acknowledged the disruptions, saying in part: “…We are working to determine the cause and extent of these service disruptions.”

Some Verizon iPhone customers were seeing SOS messages displayed in the status bar on their cell phones. The message indicates that the device is having trouble connecting to the mobile carrier’s network, but can make emergency calls over other carriers’ networks.

During cell service outages, an alternative is to connect to nearby Wi-Fi. Wi-Fi calling is also a built-in feature on most Android devices and iPhones and can be enabled through the phone settings.