A shipment of Patriot interceptors bound for Ukraine was halted for a “capability review” by Washington after the missiles had already reached Poland. The Patriot missile defense system is viewed as essential military hardware by Kiev.

“On Tuesday, US shipments that were already in Poland were halted, including more than two dozen of the Patriot’s PAC-3 missiles, more than two dozen Stinger air-defense systems, Hellfire air-to-ground missiles and more than 90 AIM air-to-air missiles, among other systems,” the Wall Street Journal reports.

In announcing the review, Pentagon spokesman Sean Parnell added, “We will not be providing any updates to specific quantities or types of munitions being provided to Ukraine or the timelines associated with these transfers.”

Missile interceptors are in short supply in the West. In May, Secretary of State and National Security Advisor Marco Rubio told Congress that “The Ukrainians asked for air defense systems – Patriot systems, which, frankly, we don’t have.”

Since making those remarks, the US has used a significant number of Patriot interceptors during the Israeli war against Iran. The US deployed a Patriot battery to Israel to defend the Jewish State from Iranian retaliatory strikes.

Additionally, the US military said it engaged in its largest Patriot battle in history to repel the Iranian missile barrage targeting an American air base in Qatar. That attack was a response to the US strikes on Iran’s nuclear facilities.

Interceptors are expensive, and the West can only produce a limited number of munitions each year. The US used as many as 89 THAAD interceptors during Israel’s 12-day conflict with Iran. The operations may have consumed over 20% of the global THAAD supply and cost the US taxpayer $1.25 billion.

While halting the arms transfer is creating panic in Ukraine, the WSJ notes Russia has developed the ability to beat the system with more maneuverable ballistic missiles and by exploiting the Patriot’s radar’s limited range.