Ukraine's President Volodymyr Zelenskyy visited the frontlines and said the conditions in the Donbas are "indescribably difficult" as Ukrainian forces try to hold out in the face of Russia's onslaught.
The Donbas region refers to the Donetsk and Luhansk provinces in the easternmost part of Ukraine. It is a major strategic, political and economic target for the Kremlin.
The Institute for the Study of War, a U.S. think tank, says Russian progress around the eastern city of Severodonetsk results largely from the fact that the Kremlin has concentrated forces, equipment and material from all other axes on this one objective.
Analysts at ISW said Ukrainian forces in Severodonetsk are facing their most serious challenge since the isolation of the Azovstal steel plant in Mariupol.