The sources declined to say how many of each munition the U.S. had left.
President Donald Trump launched the Iran war jointly with Israel in February, predicting that the conflict would last a short time.
But as the war drags on, the three people familiar with the matter expressed worry that the falling missile supplies could limit the U.S. ability to deter adversaries, including Russia and China.
A fourth person familiar with the matter said that while Central Command — which oversees U.S. forces in the Middle East — has nearly used up the land-based missiles it had before the war began, it has been able to reload from U.S. military supplies elsewhere in the world.
The sources interviewed for this story spoke on the condition of anonymity.
Asked for comment on the stockpile data, the White House issued a statement from Trump, saying the U.S. had “far more munitions than anyone in the world” and “far more than we need.”
“Our defense companies are, at this moment, making more munitions than they have ever made before, in addition to expanding their plants and equipment at record levels,” Trump said.
Analysts agree that certain munitions, including artillery shells and several types of missiles, are being produced at record levels but caution that supplies might far short of what is needed for a prolonged war.
Lockheed Martin, which makes the ATACMS and PrSMs, along with the anti-ballistic missile THAAD system, did not immediately respond to questions about Trump's statements or about supply levels. Raytheon, which makes Tomahawk missiles and Patriot interceptors, two important U.S. weapons, also did not immediately respond.
Responding to a request for comment, chief Pentagon spokesperson Sean Parnell said: “America’s military is the most powerful in the world and has everything it needs to execute at the time and place of the President’s choosing. We have executed multiple successful operations across combatant commands while ensuring the U.S. military possesses a deep arsenal of capabilities to protect our people and our interests.”
The supply figures have circulated inside the federal government over the last week during tense conversations inside the Trump administration about how much longer the U.S. can continue striking Iran without drawing down the stockpile to levels that would limit the military's ability to respond to crises elsewhere.