- Trump set the stage for clashes at the summit by writing to around a dozen allies to berate them for lagging on a 2014 pledge to try to spend two percent of GDP on defence by 2024.
- Trump has long complained that European NATO members do not pay enough for their own defence, accusing them of freeloading on America and singling out Germany for particular criticism.
US President Donald Trump launched a blistering attack on Germany at the start of a tense NATO summit Wednesday, accusing Berlin of being "captive" to Russia and demanding it and other allies immediately step up defence spending.
The two-day meet in Brussels was already shaping up to be the alliance's most difficult in years, with Europe and the US engaged in a bitter trade spat and Trump demanding that NATO allies "reimburse" Washington for the cost of defending the continent.
European alliance members were braced for criticism from Trump on defence spending, but his furious tirade at what should have been an amicable breakfast meeting appeared to take even NATO chief Jens Stoltenberg by surprise.
"Germany is a captive of Russia because it is getting so much of its energy from Russia," Trump said, taking particular aim at the proposed Nord Stream II pipeline.
"Everybody's talking about it all over the world, they're saying we're paying you billions of dollars to protect you but you're paying billions of dollars to Russia."
Trump has long complained that European NATO members do not pay enough for their own defence, accusing them of freeloading on America and singling out Germany for particular criticism.
Europe's biggest economy spends just 1.24 percent of GDP on defence, compared with 3.5 percent for the US, well below the NATO guideline of two percent.
"We're protecting Germany, France and everybody... this has been going on for decades," Trump said. "We're not going to put up with it and it's inappropriate."
NATO officials and diplomats will try to promote an image of unity at the summit in the face of growing unease about the threat from Russia, but after Trump's attack it may prove difficult to paper over the cracks.
The mercurial tycoon said before leaving Washington that his meeting in Helsinki with Russian President Vladimir Putin on Monday "may be the easiest" part of his European tour, which also includes a trip to Britain, where the government is in crisis over Brexit.
And he vowed not to be "taken advantage" of by the European Union, which he accuses of relying on the United States for defence while restricting US imports into the bloc, the world's biggest market.
'Appreciate your allies'
The meeting of 29 Western leaders has the potential to descend into another public bust-up following a divisive and bad-tempered summit of G7 nations in Canada last month.
Trump ramped up his rhetoric ahead of the talks, explicitly linking NATO with the transatlantic trade row.
"The European Union makes it impossible for our farmers and workers and companies to do business in Europe (U.S. has a $151 Billion trade deficit), and then they want us to happily defend them through NATO, and nicely pay for it. Just doesn’t work!" he tweeted as he arrived in Brussels late on Tuesday.
European officials have expressed hopes that NATO members can bridge their differences but EU President Donald Tusk launched his own salvo against Trump on Tuesday.
"Dear America, appreciate your allies, after all you don't have that many," Tusk said, before reminding Trump that European troops had come to America's aid following the September 11, 2001 attacks on the United States.
"Please remember this tomorrow when we meet at the NATO summit, but above all when you meet President Putin in Helsinki. It is always worth knowing who is your strategic friend and who is your strategic problem," he said.
Trump will meet the Russian leader in the Finnish capital on July 16 for their first summit amid an ongoing investigation in the US into possible Trump campaign collusion with Russia.
European diplomats fear a repeat of the G7, when Trump clashed with his Western allies, withdrawing from a joint statement and calling Canadian Prime Minister Justin Trudeau "dishonest and weak" before meeting North Korean dictator Kim Jong Un at a summit afterwards and praising him as "very talented".
There have been fears that Trump, keen to be seen to make a breakthrough with the Kremlin strongman, might make concessions that would weaken Western unity over issues such as Ukraine and Syria.
Trump set the stage for clashes at the summit by writing to around a dozen allies to berate them for lagging on a 2014 pledge to try to spend two percent of GDP on defence by 2024.
US ambassador to NATO Kay Bailey Hutchison told reporters that Trump would also recommit to one of the founding articles of NATO -- Article 5 -- which holds that an attack on one member is an attack on them all.