US President Donald Trump has clashed with German Chancellor Angela Merkel over Russian influence and defence spending, ahead of a Nato summit.
Mr Trump said Germany was "totally controlled by Russia" because of the high level of natural gas it imported, and this was a "bad thing for Nato".
Mrs Merkel hit back by insisting Germany was independent and defending its contribution to the alliance.
The last summit both leaders attended broke down over a trade row.
They are due to meet again in Brussels on Wednesday.
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.
He 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.
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."
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's comments were particularly stinging.
At a breakfast meeting in Brussels with Nato chief Jens Stoltenberg, the US leader said: "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."
The latest official EU figure for imports of Russian gas to Germany is between 50% and 75% (in an earlier version of this story, the figure was given incorrectly as 50.75%).
Germany has given political support for a new Baltic Sea pipeline, Nord Stream 2, which will increase the flow of Russian gas to EU states. The project has been sharply criticised by Poland and others.
The US president also accused 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".
"I want to say that I have experience of when a part of Germany was controlled by the Soviet Union," she told reporters.
"I am very happy that today we are united in freedom as the Federal Republic of Germany. Because of that we can say that we can make our independent policies and make independent decisions. That is very good, especially for people in eastern Germany."
She added that Germany put a huge proportion of its troops at Nato's disposal.
"We are still very heavily involved in Afghanistan and thus we also defend the interests of the United States of America... and Germany was pleased to do it and did it out of conviction," she said.
At the G7 summit in Canada last month, the German chancellor led efforts to reach agreement with Mr Trump on trade but the American leader rejected the summit joint communique after he left.
Mr Stoltenberg sought to play down Mr Trump's accusations, saying he expected Nato leaders would agree they were "stronger together than apart".
By Jonathan Marcus, BBC defence and diplomatic correspondent
In describing Germany as being "totally controlled by Russia" and linking this to what the US sees as Berlin's unsatisfactory defence budget, President Trump is underscoring two long-standing US concerns.
US leaders have long warned of what they see as Europe's uncomfortable dependence upon Russian energy supplies. And they have also been arguing for more than a decade that the Europeans should spend more on defence. Mr Trump has given these twin themes a new and more abrasive tone.
While he may well be overstating Germany's dependence upon Russian energy, even many European leaders are well aware of the potential influence that this could give Moscow. It's an area where short-term economic and longer-term security considerations are at variance.
No wonder then that when the US sanctions Russia for its behaviour in Ukraine and its annexation of Crimea it included steps to hamper anyone who helped build or support new Russian pipelines westwards.
German troops in Lithuania this summer
Mr Trump's 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.
Of Nato's 29 members, just five meet that target this year: the US, Greece, Estonia, the UK and Latvia. However, several, such as Poland and France are close to the mark.
Some in Nato fear Mr Trump's repeated blunt demands could harm morale, furthering the agenda of President Putin, whom they accuse of seeking to destabilise the West.
After the Nato summit on Wednesday, President Trump will spend four days in the UK before his summit with the Russian leader.