Ukraine's state-run energy company Naftogaz said one of the data centres had been hit by a "large-scale cyberattack."
"Our websites and call centre are currently down," it said on the Telegram messaging app.
Ukrainian national postal service Ukrposhta reported a "significant technical failure" in its IT systems.
"Last night there was an attack on the information infrastructure of our partners," Ukrposhta head Ihor Smeliansky said on Telegram.
The company said its specialists were working to fix the problem and restore full operation.
Ukrtransbezpeka, a state transport safety agency, which maintains the border crossing system for Ukrainian drivers, also reported problems with its data centre.
Ukrainian resources are often the target of cyber attacks, which authorities blame on Russia, which invaded Ukraine in February 2022.
Last month, services of Ukraine's biggest mobile operator Kyivstar, were knocked out after hackers used an employee's compromised account to carry out the attack.
(Reporting by Pavel Polityuk and Yuliia Dysa; Editing by Tomasz Janowski)
