"We're going to reprioritize the deliveries of these exports so that those missiles rolling off the production line will now be provided to Ukraine," particularly Patriot and NASAMS missiles, National Security Council spokesman John Kirby told reporters.

"Deliveries of these missiles to other countries that are currently in the queue will have to be delayed," he said.

Kirby said that deliveries to Taiwan -- which is preparing for a possible invasion by China -- and Israel, which faced a large-scale missile and drone attack by Iran earlier this year and is fighting a war against Hamas -- will not be affected by the decision.

Asked about the timing of the decision, the Pentagon cited Russian attacks on Ukrainian infrastructure.

"What we're seeing is Russia once again trying to destroy Ukraine's energy system and infrastructure ahead of winter, and so they urgently need... additional air defense capabilities," spokesman Major General Pat Ryder told journalists.

The decision to fast-track the munitions to Ukraine "will increase their inventories more quickly to enable them to continue to defend that critical infrastructure and the civilian population as we go into the winter," Ryder said.

The United States has been a key military backer of Ukraine, committing more than $51 billion in weapons, ammunition and other security assistance since Russia launched its full-scale invasion in February 2022.