KYIV, Ukraine (AP) — Authorities in both Ukraine and Russia say that their emergency alert mobile applications were targeted by cyberattacks late Sunday, with residents in Ukraine receiving messages that there was a high nuclear radiation danger in the capital Kyiv.

In a post late Sunday on Telegram, Ukraine’s air raid alert channel wrote that “unauthorized parties” had interfered with the messaging app’s operation, and that it had been temporarily suspended. It warned users not to click on links contained in “suspicious notifications.”

Authorities in Ukraine said the app, which Ukrainians rely on to seek safety amid daily Russian missile and drone strikes, was restored overnight. The alerts — making false claims of high radiation levels, a chemical threat and public disturbances in Kyiv — were written in English with spelling mistakes and grammatical errors as well as in a mix of Russian and Ukrainian.

One of the false posts mentioned the hacking group Hitcore. Mash, a Russian Telegram channel with links to the security services, said it had spoken to representatives of Hitcore and that they had claimed responsibility for the attack. That claim could not be independently verified.

Ukraine's state-run Center for Countering Disinformation reported the breach and urged users to monitor emergency channels on social media and rely on physical alerts while the cyberattack was being addressed.

Russian officials said Monday that hackers had sent fake emergency alerts after gaining access to the mobile app for Russia’s Emergency Ministry.

The ministry did not name who carried out the attack. In a statement, it reassured Russians that the wider public alert system was working normally, and that the mobile app acted as a supplementary service alongside alerts shared through SMS alerts, media broadcasts and municipal sirens and loudspeakers.

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