The sources, who spoke on condition of anonymity as the communications were not public, said several European countries will be affected, including in the Baltic region and in Scandinavia.
Some of the weapons in question were purchased by European countries under the Foreign Military Sales programme, or FMS, but have not yet been delivered, the sources added. Those deliveries will likely be delayed, US officials told European officials in bilateral messages in recent days, the sources said.
The White House and the state department referred queries to the Pentagon, which did not respond to a request for comment.
The delays underline the degree to which the war against Iran, which began with US-Israeli air strikes on Feb 28, has begun to stretch US supplies of some critical weaponry and ammunition.
European officials complain the delays are putting them in a difficult position.
Under the FMS programme, foreign countries purchase US-made weapons with the logistical assistance and consent of the US government.
Washington has pushed European Nato partners to purchase more US-made materiel under president Donald Trump, including through the FMS programme, as part of a bid to shift the responsibility for Europe’s conventional defence away from the US and onto European partners.
But such weapons deliveries are often delayed, causing frustration in European capitals, where some officials are increasingly looking at weapons systems made within Europe.
US officials say the weapons are needed for the war in the Middle East, and they fault European nations for not helping the US and Israel open the Strait of Hormuz.
Even before the Iranwar, the US had already drawn down billions of dollars’ worth of weapons stockpiles, including artillery systems, ammunition and anti-tank missiles since Russia invaded Ukraine in 2022 and Israel began military operations in Gaza in late 2023.
Since the start of the Iran campaign, Tehran has fired hundreds of ballistic missiles and drones at Gulf countries. Most have been intercepted, including with the PAC-3 Patriot missile interceptors that, for example, Ukraine relies on to defend its energy and military infrastructure from ballistic missiles.
The sources spoke on the condition that the names of some of the countries affected be withheld. Some share a border with Russia and, as such, the cadence of weapons deliveries can be considered sensitive defence information.
The delayed weaponry includes various kinds of ammunition, including munitions that can be used for both offensive and defensive purposes, the sources said.