The largest Ukrainian telecom operator Kyivstar reported difficulties with voice service and the use of its mobile application in a number of cities in the west and south of Ukraine on Wednesday morning.

"Dear subscribers, we know that there are currently difficulties with voice service and the mobile application in a number of cities in the west and south of Ukraine. Company specialists are working to restore services. We do our best to resolve technical issues as quickly as possible. We apologize for the inconvenience," the company said on the Facebook.

Users write in the comments under the post that there is no connection in Lviv, and it disappears in Rivne and Mykolaiv, Kirovohrad and Sumy regions. At the same time, everything is working in Ternopil and Vinnytsia. A number of users also reported problems with Home Internet in Dnipro.

Earlier, Kyivstar resumed high-speed mobile Internet in the subways of Kyiv and Kharkov. The company said it plans to achieve complete stabilization in the provision of services by the end of the week.

After a failure in the early morning of December 12, caused by a large-scale cyber attack, Kyivstar began resuming voice services on the evening of December 13; a day later, the company's mobile Internet was relaunched in some regions, and the company announced its full restoration throughout the country on the evening of December 15.

On December 17, Kyivstar restored the provision of voice services, including in roaming, mobile data transmission, Home Internet services, virtual private network (VPN) services and began resuming access to M2M (Machine-to-Machine) services for business clients. Kyivstar restored access to SMS test messaging, including international roaming, as well as M2M on December 18.