US President Donald Trump has suggested Germany's imports of Russian natural gas are a security concern, as he and other Nato leaders gather for a summit.
At talks in Brussels with Nato chief Jens Stoltenberg, he said it was a "very bad thing for Nato" that Germany was "totally controlled by Russia".
He suggested 70% of Germany's gas imports were Russian but the latest official figure was actually 50.75%.
He has accused Europeans of failing to pay enough for Nato operations.
The Brussels summit comes less than a week before Mr Trump is due to hold his first summit with Vladimir Putin, in Helsinki, reviving concerns among US allies over his proximity to the Russian president.
President Trump shocked some by quipping that the Nato summit might prove harder than next Monday's summit with Mr Putin.
European Council President Donald Tusk accused him of criticising Europe "almost daily", tweeting: "Dear America, appreciate your allies, after all you don't have that many."
Mr Tusk said the EU spent more than Russia on defence, and as much as China.
America, he added, did not and would not have a better ally than the EU, reminding Mr Trump that European troops had also fought and died in Afghanistan after the 11 September 2001 attacks on the US.
On the Putin summit, Mr Tusk said pointedly: "It is always worth knowing who is your strategic friend and who is your strategic problem."
Germany has the EU's biggest economy and has long been accused by US administrations of failing to contribute its fair share to Nato operations but Mr Trump was particularly stinging.
"Ultimately Germany will have almost 70% of their country controlled by Russia with natural gas, so you tell me – is that appropriate?" he asked at Wednesday's breakfast meeting with Mr Stoltenberg.
Germany is totally controlled by Russia because they will be getting from 60 to 70% of their energy from Russia, and a new pipeline, and you tell me if that's appropriate because I think it's not and I think it's a very bad thing for Nato."
He went on to accuse Germany of only spending "a little bit over 1%" of its economic output on defence compared to the 4.2% spent by the US "in actual numbers".
Germany actually spends 1.24% and the US 3.5%, according to the latest Nato estimate.
German Defence Minister Ursula von der Leyen rejected Mr Trump's accusations of Russian control, Reuters news agency reports.
"We have a lot of issues with Russia without any doubt," she was quoted as telling a side event at the Nato summit just after Mr Trump spoke.
"On the other hand, you should keep the communication line between countries or alliances and opponents without any question."
President Trump has said the US is being "taken advantage of" by other members of the Nato alliance, which was set up in 1949 to counter the Soviet Union, of which Russia is the main successor state.
His main objection is that all but a handful of member states have still not increased their defence budgets to meet a goal of spending at least 2% of their annual economic output on defence by 2024.