Law enforcement agencies in Arizona, Minnesota and Pennsylvania were among those that reported 911 outages Monday, although they later said service had been restored.
The Federal Communications Commission said it was "aware of the reports" and looking into the issue but did not have details as to a scope or cause.
Lumen Technologies, which is the new name for CenturyLink, said Tuesday that the outage was caused by an issue with its vendor, Intrado, and it affected seven states.
911 services in Arizona, Colorado, North Carolina, North and South Dakota, Minnesota and Utah were affected, the company said. It said the outage lasted for around an hour, from 6:30 p.m. ET to 7:47 p.m. Not all police departments in those states reported outages.
"We notified the FCC about this outage and will comply with any investigation," Lumen Global Issues Manager Mark Molzen said in a statement.
The Minneapolis Police Department was among several in that state that said service had been disrupted by Monday's outage.
Police spokesman John Elder said the outage lasted for around two hours. There were "no issues of people not getting service" due to the outage, he said by email.
Outages were also announced by police in Reno, Nevada, where the cause was under investigation. The department later said service had been restored. Tucson, Arizona, police said that there was an interruption there but service was back up.
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An outages was also reported by police in Upper Darby Township, Pennsylvania, which is near Philadelphia Monday, but service had been restored. Philadelphia police did not immediately respond to an emailed request for comment, but had not publicly reported an issue.
The New York City Police Department did not have any 911 outage, a spokesman said. Neither did the Los Angeles Police Department, police there said.
Lumen Technologies is the new brand name for CenturyLink, the telecommunication company. CenturyLink rebranded itself as Lumen earlier this month, the company said.
CenturyLink has been fined by the FCC in the past for outages that disrupted 911 service. In 2015, the company agreed to pay a $16 million penalty for an outage that affected people in seven states in 2014.
The company also had an outage on its fiber network in December 2018 that lasted almost 37 hours, and which affected 911 callers all across the country. The FCC said in a report released in August that approximately 17 million customers across 29 states lacked reliable access to 911, and at least 886 calls to 911 were not delivered. The FCC said that outage was caused by "an equipment failure that was exacerbated by a network configuration error."
Molzen said that Monday's outage "was caused by a vendor partner and services were restored in just over an hour."
"We know that when someone calls 911, seconds count and we take that responsibility seriously," he said. "Every year, we proudly process millions of calls across our robust and reliable voice network throughout the United States."
An emailed request for comment to a representative of Intrado was not immediately returned Tuesday evening.