The US-based Institute for the Study of War said that Russia has “committed a considerable amount of material, effort and manpower to manning the series of defensive positions that Ukrainian forces are currently entering”.
In addition to seizing several settlements in the south, Ukrainian forces have pressed on to shore up the war-torn eastern city of Bakhmut, captured by Russia in May.
Malayar said on Monday that Ukrainian troops were advancing south of Bakhmut and had captured a square kilometer (about a third of a square mile) there in the last week of fighting.
He also acknowledged Russian pressure to take back territory in Ukraine’s northeast, and described fighting in the Kharkiv region as “very intense” during the past week.
Ukrainian officials have estimated that Russia has deployed some 100,000 additional troops to forward positions in the northeast to apply pressure on the defensive lines.
British intelligence services have said that Russia may try to divert Ukrainian military resources by consolidating its position in Kharkiv.
While movement along the front line has been suspended, both sides have carried out air strike operations.