"Dear subscribers, we are aware that you are currently experiencing difficulties with voice communication and the mobile app in a number of cities in western and southern Ukraine," Kyivstar said on Facebook.

"The company's specialists are working to restore services. We are doing our best to fix the technical issues as soon as possible," it added.

Telecoms company Veon said on Tuesday that its unit Kyivstar had restored all communications services after they were disrupted by a mass cyberattack last week.

(Reporting by Pavel Polityuk; editing by Jason Neely)