The United States will soon be unable to provide Ukraine with certain types of ammunition that are essential to Kyiv’s battle against Russia’s invasion, as supplies are being used up faster than they can be replaced.

Washington has become by far the largest supplier of arms to Ukraine since Russia launched the invasion on February 24, with more than $16.8 billion in military assistance provided since that date.

But US stockpiles of some equipment are “reaching the minimum levels needed for war plans and training,” and restocking to pre-invasion levels could take years, Mark Cancian of the Center for Strategic and International Studies wrote in a recent analysis.

Washington is “learning lessons” from the conflict about ammunition needs in a great power war, which are “far greater” than expected, a US military official acknowledged on condition of anonymity.