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

Trump said on Monday that Washington will supply Patriot air defence 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.

U.S. officials have suggested that European countries will be willing to give up some of their own stocks of weapons for Ukraine and then buy replacements from the United States. But some of the countries involved say they still don't even know what is being asked of them, according to Reuters.