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.
Gen Tarnavskyi told the Reuters news agency that the country lacked artillery shells, particularly for its Soviet-era weapons.
"The volumes we have are not sufficient, given our needs," he said. "So, we're redistributing it. We're re-planning tasks that we had set for ourselves and making them smaller because we need to provide for them."
He said that diminishing foreign military aid was already having an impact on the battlefield, and forcing a change in tactics.