The battle for Bakhmut has become the focus of Russia's winter campaign to capture Ukraine's eastern region, with both sides describing it as Europe's bloodiest infantry battle since World War Two.
U.S. President Joe Biden will meet leaders of NATO's eastern flank on Wednesday to show support for their security after Moscow suspended a landmark nuclear arms control treaty.
Russia said on Wednesday it had broken through two fortified Ukrainian defence lines on the eastern front, with Kyiv describing conditions there as difficult and Western allies announcing more military aid including artillery rounds.
War in Ukraine is going on despite Russian leader Vladimir Putin unilaterally ordering his forces to pause attacks for 36 hours for the Orthodox Christmas.
The West needs to brace for a protracted conflict between Ukraine and Russia, NATO Secretary General Jens Stoltenberg said on Sunday, insisting that arms shipments to Kiev must continue.
Kiev said Friday it repelled a nighttime drone attack from Russia, a day after Moscow launched a new wave of missile strikes in the run-up to New Year celebrations.