Russia and Ukraine say hackers sent false nuclear attack warnings

Russia's emergencies ministry said its mobile app suffered a "massive cyberattack" on Sunday, hours after Ukraine said its own air-raid alert app had been hacked, as the two countries' longest ceasefire of the war came to an end.

Attackers sent messages through the Russian app claiming nuclear warheads had been launched at Russian regions, urging people to shelter in basements and stock up on food and water, Russia's Current Time reported. False alerts also appeared on official Telegram channels of regional emergency departments in at least nine regions, including Moscow, St Petersburg and the Sverdlovsk region, as well as a channel used by the Belgorod region's operational headquarters.

Russia's emergencies ministry said the attack did not affect its main public warning system, which uses sirens, text messages and broadcasts, and that the app was only a supplementary channel. It said its specialists were working to fix the hack, and urged people not to spread unverified information and to check threat warnings through official channels instead.

Hours earlier, Ukraine said its "Air Alarm" app had likely been tampered with after users received false warnings of radiation and chemical threats, street fighting and a supposed incoming strike by an "Oreshnik" missile, in a message written in Russian. Ukraine's air force said there was no radiation threat and the app's developers confirmed unauthorised interference; notifications were temporarily switched off before the app's normal service was restored.

Ukraine's Centre for Strategic Communications blamed Russia for the hack on its app. Russia's emergencies ministry did not say who it believed was responsible for the attack on its own system, and there is no evidence the same attackers were behind both incidents.

Separately, Poland said it had deployed extra police, including counter-terrorism units, soldiers and border guards, along its north-eastern border with Russia's Kaliningrad exclave, national police chief Marek Boroń said. He said Poland's military intelligence service and allied agencies had warned last week of possible sabotage or armed incursions in the area in the coming days, and that the operation, coordinated from a special command post at national police headquarters, covered the Podlaskie and Warmia-Masuria regions.

Boroń said the operation was preventive and that no confirmed sabotage attempt or border crossing had been reported so far. He tied the extra security to concern about sabotage, hybrid criminal activity and intelligence operations by countries to Poland's east.