This week Israel warned the United States about a critical shortage of ballistic missile interceptors amid the war with Iran, U.S. officials told the publication Semafor.

According to the outlet, Israel entered the current war already having a limited stock of interceptors, which had been depleted during last year’s conflict with Iran. One U.S. official said that Washington had known for several months that Israel’s interceptor reserves were low. “We expected this and foresaw it,” he said.

Bloomberg wrote in the first days of the war with Iran that the United States and Israel might run out of interceptor missiles. Citing a source, the agency reported that the stockpile of such missiles could be exhausted within a few days.

The New York Times also reported that Iran is using the tactic of launching large numbers of inexpensive drones in order to force the United States and its allies to spend costly air-defense missiles. According to the newspaper, Tehran’s actions raise questions about the sustainability of air-defense systems in the region during a prolonged conflict.

Bloomberg also reported that nearly two weeks after the start of the conflict, the United States is facing difficulties: Iran, whose military budget is smaller than the GDP of the state of Vermont, possesses a unique arsenal of missiles and drones that American forces have not previously encountered.