Ukraine’s largest mobile operator, Kyivstar, reported that it had experienced a powerful cyberattack on Tuesday morning, resulting in service disruptions for millions of people. The attack also affected internet access and the company stated that it was unclear when service would be restored. This interruption poses a significant danger in a country where many rely on phone alerts to warn them of impending Russian bombardments.

In a video statement, the head of Kyivstar, Oleksandr Komarov, assured that they were working to eliminate the consequences of the attack and restore communication as soon as possible. He also mentioned that users’ personal data had not been compromised. While Mr. Komarov did not explicitly say who was responsible for the attack, he indicated that the war with Russia extends into cyberspace.

The Ukrainian domestic intelligence agency, the S.B.U., announced that it would investigate the cyberattack and explore whether “Russian special services” were behind it. In the northern Ukrainian city of Sumy, the air alarm system was affected, according to local officials. Data showed a significant drop in connectivity for Kyivstar users on Tuesday, with both fixed-line and mobile services affected.

In addition to the attack on Kyivstar, one of Ukraine’s large financial institutions, Monobank, also reported being targeted by hackers. The national roaming scheme was offline on Tuesday, and public transit systems were affected in the city of Lviv.

Ukrainian telecom companies have been targeted since the full-scale invasion by Russia in February 2022, and experts state that these attacks are part of a broader campaign. Last year, Russian government-backed hackers targeted users in Ukraine more than any other country, according to a report by Google’s Threat Analysis Group. Additionally, Microsoft warned of a hacking group with ties to the Russian government preparing new cyberattacks on Ukraine’s infrastructure and government offices.