SAN FRANCISCO (CBS SF) – For more than 10 hours, thousands of T-Mobile cellphone customers in cities across the country were experiencing cellphone outages on Monday.

The carrier posted a message on its Twitter page confirming the interruption of service impacting more than 100,000 customers.

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“Our engineers are working to resolve a widespread routing issue affecting voice & text. Customers may experience longer care wait times. Please try third-party calling apps (FaceTime, WhatsApp, Signal) as a temp solution,” said president of technology, Neville Ray in a tweet around 2:45 p.m.

Other cellphone carriers were also experiencing outages Monday, though fewer than T-Mobile.

According to Down Detector, more than 22,000 customers at Metro PCS, Verizon, AT&T and Sprint customers were without cellphone service Monday afternoon.

Verizon downplayed the outage, saying its customers were only experiencing problems calling T-Mobile customers.

Some T-Mobile customers were still posting complaints online, when Neville announced service was restored.

“Voice and text services are now restored,” said Neville in his post just after 10 p.m. PST. “Thank you for your patience as we fixed the issues. We sincerely apologize for any and all inconveniences.”

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Federal Communications Commission chairman Ajit Pai called the mass outage “unacceptable” and in a Tweet said the agency will launch an investigation.

Monday’s mass outage has been linked to an unsubstantiated ‘Distributed Denial-of-Service,’ cyberattack (DDoS) on the United States.

Congressman Ted Lieu from California was one of many who shared an image from the site DDoS-tracker Digital Attack Map, showing more than 33 million simultaneous DDos attacks on the U.S.

A DDoS attack seeks to make a network unavailable to its users by flooding or disrupting the services of the host.

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Such attacks are not uncommon. In 2016, a major DDoS attack affected Twitter, Spotify, Netflix, PayPal and dozens more sites.