Finnish PM Sanna Marin has said Europe is "not strong enough" to stand up to Russia's invasion of Ukraine on its own, and has had to rely on US support.
During a visit to Australia, the leader of the pending Nato member said Europe's defences must be strengthened.
"I must be brutally honest with you, Europe isn't strong enough right now," she said. "We would be in trouble without the United States."
The US is by far the largest provider of military assistance to Ukraine.
Since the start of the war in February, it has committed $18.6bn (€17.7bn; £15.2bn) in support, a research briefing last month by the UK's House of Commons said.
The second largest donor is the European Union, followed by the UK, the Kiel Institute for the World Economy says. But their contributions are dwarfed by those of the US.