After the summit Trump will meet Russian President Vladimir Putin in Helsinki on Monday.
U.S. President Donald Trump accused Germany of being a "captive" of Russia on Wednesday as Western leaders gathered in Brussels for a NATO summit where Trump wants Europeans to pay up more for their own defence.
In a startling public outburst, Trump told NATO Secretary-General Jens Stoltenberg that Germany was wrong to support a new 9.4 billion euro Baltic Sea pipeline to import Russian gas while being slow to meet targets for contributing to NATO defence spending that was intended to protect Europe from Russia.
"We're supposed to be guarding against Russia and Germany goes out and pays billions and billions of dollars a year to Russia," Trump said in the presence of reporters at a pre-summit meeting at the residence of the U.S. ambassador to Belgium.
His comments appeared to substantially overstate German reliance on Russian energy and to imply the German government was funding the pipeline, which is a commercial venture.
With tensions in the Western defence alliance already running high over Trump's demands for more contributions to ease the burden on U.S. taxpayers, and a nationalistic stance that has seen trade disputes threaten economic growth in Europe, the latest remarks will fuel concerns among allies over the U.S. role in keeping the peace that has reigned since World War Two.
After the two-day summit in Brussels, Trump will meet Russian President Vladimir Putin in Helsinki on Monday.
German Defence Minister Ursula von der Leyen hit back at Trump's remarks: "We have a lot of issues with Russia without any doubt," she told reporters in English. "On the other hand, you should keep the communication line between countries or alliances and opponents without any question."
Stoltenberg later told reporters that Trump had used "very direct language" but that all NATO allies were agreed that the cost of defence spending must be spread around and that last year had seen the biggest increase in a generation.
"Despite disagreements, I expect that we will agree on the fundamentals that we are stronger together than apart," he said.
Trump said Germany's closure of coal and nuclear power plants on environmental grounds had increased its dependence, like much of the rest of Europe, on Russian gas.
Trump said: "We're protecting Germany, we're protecting France, we're protecting all of these countries. And then numerous of the countries go out and make a pipeline deal with Russia where they're paying billions of dollars into the coffers of Russia ... I think that's very inappropriate."
German Chancellor Angela Merkel, who meets Trump at the summit, has given political backing to the Nord Stream 2 pipeline to import more gas, despite criticism from other EU governments. However, Berlin insists it is a privately funded commercial project with no input of public money.
Trump said: "If you look at it, Germany is a captive of Russia. They got rid of their coal plants, they got rid of their nuclear, they're getting so much of their oil and gas from
Russia. I think it is something NATO has to look at."
However, his comment that "Germany is totally controlled by Russia because they are getting 60 to 70 percent of their energy from Russia and a new pipeline" appeared to mis-state German energy use - about 20 percent of which is accounted for by oil and gas imports from Russia.
Trump also renewed his call for other NATO allies, including Germany, to "step it up" and pay in more to the Western alliance after years in which U.S. taxpayers have, he said, borne an "unfair" share of military spending
"They have to step it up immediately. Germany is a rich country, they talk about increasing it a tiny bit by 2030. Well they could increase it immediately, tomorrow, and have no problem," Trump said.