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.
Perhaps now folks can see why we were judging European nations so hard for failing to keep up with their NATO obligations. It's a lot more expensive in the end and less effective to be trying to stand up production now.
It's the worst type of I told you so because it involves something that really needs to happen for everyone. I just hope that production picks up and Israel cools down for the spring.
We need sustained and modern shell production moving into the future, not only to replenish current stocks and supply Ukraine now, but to ensure scalable production in future conflicts.