Three people familiar with internal information said the United States had used nearly all of its stocks of key precision land-attack missiles during the five-month conflict with Iran.
They identified the weapons as Army Tactical Missile Systems, known as ATACMS, and Precision Strike Missiles, or PrSM.
ATACMS is being phased out in favor of the newer PrSM, whose initial stockpile was smaller and for which the U.S. Army has placed substantial orders for 2027.
A fourth person familiar with the matter said U.S. Central Command had nearly exhausted its pre-war supply of land-based missiles and was drawing replacements from U.S. bases elsewhere.
The sources did not disclose the size of the U.S. inventories or the number of missiles remaining.
CSIS estimated that about 65% of U.S. Patriot interceptors were used between February and July, while THAAD stocks fell by at least 38% from levels at the start of the war.
Patriot and THAAD are air- and missile-defence systems designed to detect and destroy airborne threats.
President Donald Trump said the United States possessed more weapons than any other country and more than it needed.
Pentagon spokesman Sean Parnell said the military retained sufficient and deep capabilities while conducting operations across multiple combat commands.
The reason for a reported decision to defer another major attack inside Iran remains disputed.
Accounts cited by the supplied material linked the decision to warnings from military advisers about arsenal pressures, while a U.S. official said pressure from Gulf countries was the reason.
Analysts cited in the material said production of some munitions was at record levels but remained below the pace required for a prolonged war.