(Reuters) - Ukraine's biggest mobile network operator Kyivstar aims to restore some of its services later on Wednesday after an "unprecedented" cyber attack, the company's CEO Oleksandr Komarov said.
Tuesday's attack on Kyivstar, which has 24.3 million mobile subscribers and more than 1.1 million home internet subscribers, knocked out services, damaged IT infrastructure and air raid alert systems in some of the regions. It appeared to be the largest attack since Russia's full-scale invasion of Ukraine in February 2022.
"We expected that we would be able to return some services in the first half of the day today. We see that this will not happen, but we are moving towards starting to restore some services in the second half of the day," Komarov said in televised comments.
He added the company faced obstacles that prevented restoration work from moving faster, and said the level of attack was unprecedented.
In a separate statement on Facebook (NASDAQ:META), Kyivstar, owned by Amsterdam-listed mobile telecoms operator Veon, reiterated that personal client data was safe, and systems storing it were not damaged.
Ukraine's SBU intelligence agency told Reuters it was investigating the possibility Russian security services were behind the attack.
Moscow had no immediate comment.
Russian hacktivist group Killnet on Tuesday claimed responsibility for the attack via a statement on the Telegram messaging app, but did not provide evidence.
On Wednesday, a group called Solntsepyok, which translates as 'Sun Blaze', also claimed responsibility, posting screenshots that appeared to show they had access to Kyivstar's servers.
Ukraine's SBU also said on Wednesday that one of the Russian groups claimed responsibility, saying it was a hacking unit of Russia's military intelligence service GRU.
Activist hacking groups routinely make difficult-to-prove claims about major digital disruptions. Reuters could not immediately verify the authenticity of the claims.