Several European countries said on Tuesday they were willing to buy U.S. arms for Ukraine under a plan announced by U.S. President Donald Trump, although arrangements still needed to be worked out.

Trump said Monday that Washington will supply Patriot air-defense systems, missiles and other weaponry to Ukraine for its war against Russia’s invasion and that the arms would be paid for by other NATO countries.

But much remains undisclosed, including the amounts and precise types of weapons to be provided, how quickly they would be supplied and how they would be paid for.