Ukraine’s biggest wireless network operator said attackers knocked its service offline Tuesday, disrupting banks and other businesses in an event that coincided with the Ukrainian president’s latest visit to Washington. 

The incident, which affected millions of Kyivstar customers in Ukraine, is among the most disruptive cyberattacks to succeed against the country’s civilian infrastructure since the start of Russia’s invasion of the country in 2022. Officials in the Kyiv region said that the air alert system that warns residents about missiles was temporarily disabled due to the hack.