Late Sunday, Ukrainian users of the “Air Alert” app received unusual messages warning of a radiation threat in Kyiv, a chemical attack, and street fighting in the city. One message, written in Russian, claimed a nuclear alert had been declared across Ukraine and referenced Russia’s Oreshnik hypersonic missile. The alerts were unusual in both tone and language, prompting suspicion among users. The air force said the app had likely been “compromised by the enemy” and urged people to remain calm.

Ukraine’s air force said the app had been temporarily suspended after unauthorized parties interfered with its operation. It warned users not to click on suspicious links and confirmed there was no radiation threat. The Center for Countering Disinformation also issued a statement urging people to rely on official social media channels and physical alerts during the disruption.

Russia’s Ministry of Emergency Situations reported that its mobile alert app had been hit by a “massive cyberattack,” resulting in the spread of fake information. The ministry downplayed the impact, stating the app was a supplementary service and that the main alert system remained functional. It called on the public to rely on official sources for information.

A fake message sent through the Russian app warned of nuclear warheads being launched at all Russian regions and advised citizens to stock up on food and take shelter. The message was informal and contained profanities and derogatory language about Russian regions. The ministry said it was working to restore the app to normal operation.

Many Kyiv residents were unfazed by the false alerts and even shared memes online, mocking the idea of a nuclear threat. Artem Pyndyk, a 37-year-old businessman, said the alerts did not trigger the kind of reaction the attackers likely expected. Oksana Vostrykova, a pizzeria employee, said she immediately suspected the messages were fake and did not panic.

The cyberattacks occurred hours after a six-day humanitarian ceasefire in the occupied Kherson region ended. The truce allowed the evacuation of hundreds of residents from the besieged town of Oleshky. Ukrainian authorities said the ceasefire had allowed Russia to replenish its drone defenses and ammunition supplies.

While the pro-Kremlin Telegram channel Mash reported that a group called Hitcore claimed responsibility for the Ukrainian attack, this claim could not be independently verified. Russian authorities did not name any group responsible for the cyberattack on their app, only stating that “malicious actors” were behind it. Neither side provided evidence to support their accusations.

Ukraine’s air force said the attack did not affect military command systems, while Russia’s emergency ministry said the app was a supplementary service. The incidents highlight the vulnerability of civilian communication infrastructure in the context of ongoing conflict.