Ukrainian forces were holding just 20 percent of the eastern city of Sievierodonets, but there was still hope that they could prevent Russia from taking complete control, the head of the city administration told Reuters in a telephone interview on Wednesday.

Russian forces control 60 percent of the city, while the rest has become "no man's land," said Oleksandr Stryuk, the Ukrainian head of the city administration, who declined to give his location.