“Our goal is not to hurt anyone. It’s just to not empower the Russian government to have another tool in their war chest,” Schaeffer said in an interview with The Washington Post.

Cogent, based in Washington, D.C., is one of the world’s largest providers of what’s known as Internet backbone — roughly comparable to the interstate highway system, providing the primary conduit for data flows that local companies then route to individual domains. Schaeffer said Cogent’s networks carry about one-quarter of the world’s Internet traffic. Cogent has several dozen customers in Russia, with many of them, such as state-owned telecommunications giant Rostelecom, being close to the government.

Russia, like most nations, is connected to the world by several backbone providers, but Cogent is among its largest. The company began terminating its Russian companies at noon Friday but was doing so gradually. Some customers asked for a delay of up to several days while they found other Internet sources, Schaeffer said, and the company is trying to accommodate those requests.

“We’re pretty confident that we’re not interfering with anyone’s ability to get some information,” he said, though he acknowledged the likelihood of slowdowns and other disruptions with Russia.

In a letter sent Thursday to one of Cogent’s Russian customers and obtained by The Washington Post, the company wrote, “In light of the unwarranted and unprovoked invasion of Ukraine, Cogent is terminating all of your services effective at 5 p.m. GMT on March 4, 2022. The economic sanctions put in place as a result of the invasion and the increasingly uncertain security situation make it impossible for Cogent to continue to provide you with service. All Cogent-provided ports and IP address space will be reclaimed as of the termination date.”

Ukrainian officials have been lobbying American Internet companies to cut off services from Russia and also asked ICANN, the California-based nonprofit group that oversees aspect of Internet functionality worldwide, to suspend the main Russian Internet domain, .ru. On Wednesday, ICANN rejected the request.

While Ukraine’s calls for curbs on online sources to Russian government propaganda have generated wide sympathy and some action by key American companies, the effort to cut off Russia from the Internet overall has generated significant backlash from digital rights advocates. They argue that isolating Russians from online services — and especially social media — deprives them of access to information about the war in Ukraine, leaving government-controlled media as the only source of news.

“This move by Cogent is misguided. Cutting the Russian people off from the global internet harms those who seek to obtain and share truth,” tweeted Rebecca MacKinnon, vice president at the foundation that hosts Wikipedia. “Including many Wikpedians contributing to the page about Russia’s invasion of Ukraine, despite govt threats.”

News of the looming Cogent action began spreading on Thursday after Mikhail Klimarev, executive director of the Internet Protection Society, which advocates for digital freedoms in Russia, posted a copy of Cogent’s termination letter to a Russian client to his Telegram channel.

“Very bad news,” Klimarev wrote in his Telegram post. “I will be glad if it is not confirmed.”

But soon it was. Telecommunications analysts were closely tracking events on Friday to see how extensively Cogent’s action was affecting Internet service in Russia. Doug Madory, director of Internet analysis for the Web monitoring firm Kentik, wrote in a blog post, “A backbone carrier disconnecting its customers in a country the size of Russia is without precedent in the history of the internet.”

Other U.S. backbone providers have been debating cutting off Russian customers in recent days, and any following Cogent’s lead would amplify the impact.

Lumen Technologies, another major connection for Rostelecom, declined to say whether it might do so. But it said it was not taking on new Russian business.

“Lumen has stopped the sale of all new products and services to both Russian-based companies and non-Russian based companies where the services will be provided in Russia,” the company said, adding that it had terminated a deal to provide services to one Russian financial institution.

Network security researcher Barrett Lyon said Cogent’s move alone would immediately affect traffic from North America, causing connections across the Atlantic to lag, especially in video. Russians trying to watch streaming video from the United States are expected to see the deterioration first.

“Cogent is usually seen as a lower-cost network option. As a result, they end up carrying a lot of traffic for video and low-cost packets,” Lyon said. “That traffic will reconverge to other networks and redistribute, causing a huge network load across networks willing to carry traffic for Rostelecom.”

As of Friday morning, Cogent had direct connections to more than 6,000 network blocks, or large chunks of Internet addresses, handled by Rostelecom, one of the largest swaths from the United States.

Earlier on Friday, as Rostelecom announced its fourth-quarter earnings, it said it would hold off on projecting future results because of the uncertainty sparked by the Ukraine conflict.

This is a developing story. Please check back for updates.