Emergency alert applications used to warn citizens about attacks in Russia and Ukraine have reportedly come under cyberattacks, with false warnings about nuclear and chemical threats sent to residents in and around Kyiv.

Kyiv initially reported that its emergency alert application had been hacked. Several hours later, Moscow also announced that its own alert app had been targeted in what it described as a “massive cyberattack”.

Russia’s Ministry of Emergency Situations said in a Telegram post early Monday that the cyberattack had caused false information to circulate through the application. However, the ministry did not identify those responsible.

Ukraine’s Centre for Strategic Communications blamed Russia for the hacking in a post on X.

On Sunday evening local time, Ukraine’s Air Force reported that users had received fabricated alerts warning of potential nuclear and chemical attacks in Kyiv and surrounding areas. Messages also warned of possible clashes on the streets.

Another false notification claimed that Russia had deployed its Oreshnik hypersonic missile.

The Ukrainian Air Force later issued a message on Telegram, telling citizens that the alert application appeared to have been subjected to “enemy interference”. It assured the public that there was no radiation threat.

The cyberattack announcements from Russia and Ukraine came shortly after a ceasefire expired in part of the Moscow-occupied Kherson region. The ceasefire had begun the previous Tuesday.