WASHINGTON (AP) — The U.S. military is experiencing a “beyond critical” shortage of advanced missile interceptors in Europe largely driven by President Donald Trump’s war with Iran, a U.S. defense official in Europe and a NATO official told The Associated Press, raising concerns about vulnerabilities in NATO countries to a potential Russian attack.

The U.S. defense official said the most concerning shortfall involves Patriot missile interceptors, which can shoot down Russia’s high-speed ballistic missiles. The NATO official confirmed the low inventories of Patriots among American and NATO forces in Europe. Both spoke on condition of anonymity to discuss sensitive military matters.

In the event of a Russian ballistic missile assault on, for example, a military headquarters or power plant, NATO could be in a similar position to Patriot-starved Ukraine and be forced “to take punch after punch in the mouth,” the U.S. defense official said.