Ukraine’s military intelligence agency (HUR) said on Sunday it hacked Russia’s Central Election Commission and other government services in response to voting in occupied Ukrainian regions.

The operation coincided with Russia’s “unified voting day,” when regional and local elections are held simultaneously across the country. This year, ballots were also cast in Crimea and other occupied parts of Ukraine. Kyiv and its allies say those elections are illegal.

HUR said its distributed denial-of-service (DDoS) attack targeted the servers of the CEC, Russia’s electronic voting system, the state services portal Gosuslugi and core routers of state-run telecoms provider Rostelecom. DDoS incidents flood servers with traffic with the intention of knocking them offline.

“The goal was to disrupt online voting, particularly in occupied Ukrainian regions,” a HUR spokesperson said, adding that the attacks temporarily paralyzed digital services and left many Russians unable to vote electronically.

Russia acknowledged its election-related websites had come under sustained attack.

CEC chief Ella Pamfilova told local state media that since the start of the voting on Friday, CEC website was intermittently unavailable but stressed that voting itself had not been affected.

Deputy Digital Development Minister Oleg Kachanov confirmed “short-term traffic degradation” on Gosuslugi and the CEC’s digital services but said the remote voting platform functioned as designed.

Rostelecom president Mikhail Oseevsky said the routers supporting the CEC website were overloaded and had to be rebooted, causing disruptions during peak hours. “These problems have now been resolved,” he said, adding that Russia would reinforce defenses ahead of parliamentary elections next year.

Pamfilova later told reporters that more than 500,000 attacks had been logged against the CEC’s resources over the three-day voting period.

Ukraine’s foreign ministry denounced the elections held in occupied territories as illegal and called on allies not to recognize their results.

The European Union echoed the criticism, with a spokesperson saying the bloc “does not recognise either the so-called ‘elections’ or their results in the occupied territory,” calling the vote “another violation of international law.”