Sources: 

The U.S. government has alerted European allies, including the UK and Poland, regarding significant delays in arms shipments due to ammunition depletion from the ongoing Iran war. Reports indicate that Washington has warned European nations to expect these postponements as they scramble to replenish inventory levels.
According to a Financial Times report, this warning covers various nations, including Lithuania and Estonia.
U.S. officials have cited a substantial increase in weapons used in the last two months in Iran as a primary factor driving these delays. As a result, contracted deliveries of essential munitions are likely to be postponed, raising acute concerns about U.S. inventories.
Furthermore, the stockpile issues will impact munitions for critical systems, including Himars and Nasams, necessary for operational readiness in the ongoing geopolitical situation.
The Pentagon confirmed it is carefully evaluating both new requests from partners and existing arms transfer cases to ensure alignment with military needs, reflecting the urgency of the situation as the U.S. may face a prolonged conflict in the Middle East while also addressing challenges in the Indo-Pacific region.
A senior Ukrainian official has indicated that U.S. weapons intended for Kyiv have also faced delays since the onset of the Iran war, further complicating the defense support landscape in Europe.
Sources: 
The U.S. has warned European allies, including the UK and Poland, of potential delays in arms shipments due to stockpile depletion from the ongoing war in Iran. These delays are affecting munitions for various missile systems, raising concerns over U.S. inventory levels amid heightened military needs.