Warmer weather is now creating muddy conditions in Ukraine's eastern region, making it difficult for troops to get around there, which analysts say could cause a stalemate.
Russian forces are trying to encircle the Ukrainian stronghold of Bakhmut. This reportedly follows a major setback for Russia elsewhere in the Donetsk region.
Russia lost at least 130 tanks and armored personnel carriers in a three-week battle in Vuhledar, according to the New York Times that quoted the Ukrainian military.
The British defense ministry says satellite pictures appear to show an elite Russian unit lost many vehicles near the town.
The ministry also says muddy conditions will hamper the off-road movement of heavier armored vehicles, especially over churned-up ground in the Bakhmut area.