Just before Russian troops pushed across the Ukrainian northern border this month, members of Ukraine’s 92nd Assault Brigade lost a vital resource. Starlink satellite internet service

, which soldiers use to communicate, collect intelligence and conduct drone attacks, had slowed to a crawl.

Operated by Elon Musk’s SpaceX, Starlink has been critical to the Ukrainian military since the earliest days of the war with Russia. Without the full service, Ukrainian soldiers said, they couldn’t quickly communicate and share information about the surprise onslaught and resorted to sending text messages. Their experiences were repeated across the new northern front line, according to Ukrainian soldiers, officials and electronics warfare experts.

At the heart of the outages: increased interference from Russia.

As Russian troops made gains this month near Kharkiv, Ukraine’s second-largest city, they deployed stronger electronic weapons and more sophisticated tools to degrade Starlink service, Ukrainian officials said. The advances pose a major threat to Ukraine, which has often managed to outmaneuver the Russian military with the help of frontline connectivity and other technology, but has been on the defensive against the renewed Russian advance.

The new outages appeared to be the first time the Russians have caused widespread disruptions of Starlink. If they continue to succeed, it could mark a tactical shift in the conflict, highlighting Ukraine’s vulnerability and dependence on the service provided by Mr. Musk’s company. As the United States and other governments work with SpaceX, the disruptions raise broader questions about Starlink’s reliability against a technically sophisticated adversary.

Starlink works by beaming an internet connection down from satellites revolving around Earth. The signals are received on the ground by pizza-box-size terminal dishes, which then distribute the connection like a Wi-Fi router to laptops, phones and other devices nearby. Starlink has provided Ukraine with vital internet service since 2022, with soldiers relying on it to guide internet-connected drones that are used for surveillance and as weapons, among other tasks.

In an interview this week, Mykhailo Fedorov, Ukraine’s digital minister, said Russia’s recent attacks against Starlink appeared to use new and more advanced technology. The service previously held up remarkably well against interference on battlefields, where there has been widespread electronic warfare, radio jamming and other communication disruptions.