Ukraine's biggest mobile network operator has been hit by what appeared to be the largest cyberattack of the war with Russia, knocking out mobile and internet services for millions and the air raid alert system in parts of the Kyiv region.
Kyivstar has 24.3 million mobile subscribers - more than half of Ukraine's population - as well as more than 1.1 million home internet subscribers.
Its CEO Oleksandr Komarov said the attack was "a result of" the war with Russia although he did not say which Russian body he believed to be responsible, and that the company's IT infrastructure had been "partially destroyed".
"War is also happening in cyberspace. Unfortunately, we have been hit as a result of this war," he told a television broadcast.
Ukraine's SBU intelligence agency told Reuters one of the possibilities it was investigating was that of a cyberattack by Russian security services.
Russia's foreign ministry did not immediately respond to a request for comment.
Komarov said it was unclear when Kyivstar would be able to restore connection.
"(The attack) significantly damaged (our) infrastructure, limited access, we could not counter it at the virtual level, so we shut down Kyivstar physically to limit the enemy's access," Komarov said.
Russian hacktivist group Killnet claimed responsibility for the attack in a statement on Telegram, but did not provide evidence.
A source close to Ukraine's cyber-defence said Russia was suspected to be the source of the attack but no specific group had been identified.
Ukrainian officials said air raid alert systems in more than 75 settlements in the central Kyiv region were affected by the cyberattack.
Kyivstar, owned by Amsterdam-listed mobile telecoms operator Veon, said in a statement on Facebook that it was working to repair the outage and was co-operating with law enforcement bodies.
Komarov said two databases containing customer data had been damaged and were currently locked.
Separately, the co-founder of Monobank, a major Ukrainian payment system, said in a social media post that his company was suffering a distributed denial of service attack, but everything was "under control".
Representatives of PrivatBank and Oschadbank, two major Ukrainian financial institutions, said part of their ATM machines and card terminals had been affected by the Kyivstar outage.
Ukrainian state bodies and companies have often accused Russia of orchestrating cyberattacks against them in the past.