A person walks by a Verizon store in Manhattan, New York City, U.S., November 22, 2021.
The outage first began at 9:30 AM ET and reached its peak at 11:19 AM, during which time 105,000 complaints were logged. Reuters / ANDREW KELLY

Verizon's services have returned to normal after a technical issue disrupted its network, affecting hundreds of thousands of customers across the United States on Monday.

Users in Chicago and Seattle were among the worst hit, with some iPhone users reporting that their devices displayed "SOS" mode, Reuters reported.

The Federal Communications Commission (FCC) said earlier on Monday that it was monitoring the situation to understand the cause of the outage. "We're aware of a Verizon outage impacting customers in parts of the country," it stated. "We are working to determine the cause and extent of these service disruptions."

According to DownDetector, a site that monitors service outage complaints, the disruption began at 9:30 am ET and reached its peak at 11:19 am, during which time 105,000 complaints were logged. By 5:02 pm, the total number of reports decreased to 28,842, indicating that the many users continued to experience outages throughout the day.

Verizon serves 114.2 million subscribers in the U.S. and is the latest to report service disruption this year after AT&T and Microsoft.

In response to reports from several iPhone users about "SOS" mode appearing in the status bar, Apple clarified that if the device is not connected to a cellular network, users can still make emergency calls through other carriers.

Taking to X on Monday evening, Verizon stated that its service has returned to normal levels.

"Verizon engineers have fully restored today's network disruption that impacted some customers. Service has returned to normal levels. If you are still having issues, we recommend restarting your device," the company stated.

Meanwhile, AT&T users reported 448 outage complaints by 5:15 pm ET, although the carrier denied there was a nationwide service disruption, according to Reuters. This outage adds to the growing list of cell service disruptions experienced this year.

In February, AT&T had a 12-hour outage that affected more than 70,000 customers. During this outage, more than 92 million voice calls were blocked, including 25,000 attempts to reach 911 emergency assistance. The FCC is probing the massive outage.

AT&T users encountered similar disruptions in June and August, while a major network issue in July impacted Microsoft systems globally due to a glitch associated with an update from the cybersecurity group CrowdStrike.

Microsoft