A top general says diminishing foreign military aid is already having an impact on the battlefield.
Ukraine has warned it is already being forced to downsize some military operations because of a drop-off in foreign aid.
Top general Oleksandr Tarnavskyi said troops faced ammunition shortages along the "entire front line", creating a "big problem" for Kyiv.
It comes as billions of dollars of US and EU aid have been held up amid political wrangles.
Ukraine said it hoped to boost its own ammunition industry with western help.
But it relies heavily on western supplies, particularly on deliveries of long-range missiles and air defence systems, to fight occupying Russian forces.