Ukraine is addressing its manpower challenges by forming new brigades, but delays to Western supplies of weapons are likely preventing them from being properly equipped, according to military analysts.
The Institute for the Study of War said Kyiv is relying on "timely and appropriate Western security assistance".
It described prompt aid from Ukraine's allies as a "crucial determinant of when and at what scale Ukrainian forces can contest the battlefield initiative and conduct operationally significant counteroffensive operations in the future".
It comes after Volodymyr Zelenskyy told Bloomberg TV that Ukrainian forces were better positioned in terms of manpower than a few months ago - but any future counteroffensive was dependent on brigades having heavy equipment and artillery.
The Ukrainian president said military equipment pledged by the US was taking too long to arrive on frontlines.
"This is the biggest tragedy of this war, that between the decision and real fact, we have a real long, long, long wait," Mr Zelenskyy said.
