Russia and Ukraine have both reported cyberattacks targeting their emergency alert apps, with hackers sending fake warnings of nuclear, chemical and radiation threats to mobile phone users.

While Ukraine’s air raid alert system briefly flashed warnings of a possible nuclear threat and street combat, Russia’s emergency ministry said its app was hit by a “massive cyberattack” that allowed attackers to spread false information to the public.

Ukraine first reported that its air raid alert system had been hacked, sending warnings of alleged chemical and radiation threats to mobile phones across the country. The loudspeaker alert system was also compromised, broadcasting similar messages through loudspeakers across Kyiv, Fox News reported.

The app for a short time showed Kyiv and other areas subject to nuclear and chemical alerts and the threat of street combat. An erroneous message said Russia’s hypersonic Oreshnik missile had been deployed, according to Reuters.

“The Air Alarm application has probably been subjected to hostile interference. There is no radiation threat! Stay calm and follow our updates on our channel,” an alert posted on Telegram read.

The incidents and false warnings came minutes before a ceasefire in the Ukrainian frontline city of Oleshky was due to end. US First Lady Melania Trump had secured a ceasefire between Russia and Ukraine in Oleshky. The ceasefire began on October 27 and ended on November 1.

“Attention. The Air Alert app has likely been compromised,” the Air Force said on Telegram, adding that there was no radiation threat and urging people to stay calm and follow official updates, according to news agency ANI.

However, Ukraine’s Ministry for Digital Transformation later said in a post on X that the nationwide alert system was functioning normally.

“The nationwide alert system is operating in normal mode. All threat signals are transmitted to regional administrations and, accordingly, to street alert systems,” the ministry said.

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“The Russian Ministry of Emergency Situations’ mobile app was subjected to a massive cyberattack, which allowed the attackers to distribute fake information to the public,” the ministry said in a statement.

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The ministry later said its public alert system is “operating as normal”, stressing that citizens are informed of alerts through multiple channels including sirens and loudspeakers, text messages, and TV and radio broadcasts, and that the app is “only an additional, ancillary news service,” BBC reported.

“The hacking of the mobile app has not had, and cannot have, any impact on the operation of the public alert system,” the ministry said on its Telegram channel.

It also shared an image showing some of the alerts that had appeared on Ukraine’s air raid warning app and urged residents to disregard any unusual messages they might receive through the application, according to BBC.

Russia did not immediately identify who might have been behind the cyberattack.

(With inputs from BBC, ANI)