Ukraine war: Major internet provider suffers cyber-attack
The company said it restricted customer access to protect military users and critical infrastructure.
Global internet monitor Netblocks said it was the most severe disruption to affect Ukrtelecom since Russia's invasion of Ukraine started last month.
Netblocks said it saw a collapse in connectivity to 13% of pre-war levels.
However, Ukrainian users on different internet providers, who spoke to the BBC, reported no problems.
Ukrtelecom says it is the country's biggest provider of fixed internet in terms of geographical coverage, but second after Kyivstar in terms of number of clients.
It told the BBC it had been operating at about 80% of its full coverage because of damage caused by the Russian invasion.
In a statement Ukrtelecom chief executive Yuriy Kurmaz wrote that a powerful enemy cyber attack was carried out on Ukrtelecom's IT infrastructure.
"In order to protect the critical network infrastructure and not interrupt services to the Armed Forces, other military bodies and users of critical infrastructure, we were forced to temporarily restrict internet access to most private users and business customers," he added.
Mr Kurmaz said the attack had been successfully repulsed and the provision of services was being gradually resumed.

Yuriy Shchyhol head of Ukraine's State Service for Special Communication and Information Protection said that its specialists had responded quickly to the situation, and had driven-back the attack. Read More…