Stopping the delivery of munitions and other military aid including air defense systems likely would be a blow to Ukraine as it contends with some of Russia's largest missile and drone attacks of the three-year-old war.

"This decision was made to put America's interests first following a DOD (Department of Defense) review of our nation's military support and assistance to other countries across the globe," White House Deputy Press Secretary Anna Kelly told AFP in an email.

The curtailment of military aid signals a possible shift in the priorities of US President Donald Trump, who has pressed for Russia and Ukraine to speed up stalled peace talks.

The Republican has moved on to playing a greater role in orchestrating a possible ceasefire in Gaza and toning down Iran-Israel tensions after a deadly 12-day conflict between the arch foes.

The Pentagon review determined that stocks had become too low on some previously pledged munitions, and that some pending shipments now would not be sent, said a US official who spoke on condition of anonymity, according to Politico which first reported the halt of military aid.

"The strength of the United States Armed Forces remains unquestioned -- just ask Iran," Kelly said, making a reference to the recent US bombings and missile strikes against the Islamic republic's nuclear facilities.

Politico and other US media reported that missiles for Patriot air defense systems, precision artillery and Hellfire missiles are among the items being held back.

Last week at a NATO summit in the Netherlands, Ukrainian President Volodymyr Zelensky met with Trump and appeared to get a vague response from the US leader on Patriot air defense systems.

"We're going to see if we can make some available," Trump said of the missiles that Kyiv desperately seeks to shoot down Russian attacks.

"They're very hard to get," Trump added.

Asked by AFP for comment on the halt of shipments and why it was occurring, the Pentagon did not respond directly.

But its chief spokesman Sean Parnell said "America's military has never been more ready and more capable thanks to President Trump and Secretary (Pete) Hegseth's leadership."