Hadja Lahbib, Belgium’s foreign minister, warned: “It is dangerous to make promises that we cannot keep.”

Some West European countries worry that giving NATO that much money and power would undermine efforts for the European Union to play a larger role in defense.

The NATO proposal also threw up a lot of questions on the details. A key issue is whether the financial target consists of fresh money, or is merely made up of existing programs that allies are sending individually to Ukraine.

Diplomats cautioned that the discussion on financing remains at a very early stage, pointing to Stoltenberg’s refusal to publicly acknowledge the amount involved in his proposal.

 Jan Lipavský, the Czech foreign minister, said: “We do welcome the initiative and we need to see practicalities and the details.”

Spanish Foreign Minister José Manuel Albares said: “We need to calculate how much Ukraine needs to keep its democracy, sovereignty and territorial integrity. And when we have that amount, we have to decide how we can get it.”