"Many countries are not paying what they should, and, frankly, many countries owe us a tremendous amount of money from many years back", Trump said at a breakfast meeting with NATO Secretary-General Jens Stoltenberg.
'We are supposed to be guarding against Russian Federation and Germany goes out and pays billions and billions dollars a year to Russian Federation, ' he said. "It's very unfair to our taxpayers". In recent weeks, various European leaders have also threatened to retaliate against US tariffs and filed complaints to the World Trade Organization.
Trump is reportedly considering imposing sanctions on the five European countries involved in the pipeline project. Journalists will not be allowed to cover either meeting, she said.
Mr Stoltenberg also stressed how "even during the Cold War, NATO allies were trading with Russia". "We have highlighted the importance of this diversification of supplies to make sure that our energy systems are resilient".
"You can expect to hear a lot about that - other countries taking on a bigger role and doing more", the official said.
Many US presidents have urged European governments to spend more on their militaries.
"I really can't say right now. He may be the only one, but that's OK with me".
Just moments before flying off, Trump took aim at the already vulnerable May, saying that it is "up to the people" to determine whether she should stay in power. "We are being taken advantage of by the EU".
European officials say while U.S. defence spending makes up 70 percent of combined allied governments' military budgets, just 15 percent of USA expenditure is spent in Europe on NATO-related defence.
Trump has, meanwhile, delivered on US commitments to Europe.
"Dear America, appreciate your allies, after all you don't have that many", Tusk said, before reminding Trump that European troops had fought alongside Americans in Afghanistan following the September 11, 2001 attacks on the United States.
However new figures published Tuesday will do little to satisfy Trump's demands - they show that only seven European NATO countries will reach the two percent target in 2018.
While leaving the White House on Tuesday to travel to Europe for a week of meetings with North Atlantic Treaty Organisation allies and, later, a Finland summit with Russian president Vladimir Putin, President Trump made an odd pronouncement: that his upcoming meeting with Putin would be the easiest of the bunch.
German Defence Minister Ursula von der Leyen dismissed the president's claim. "As far as I'm concerned, a competitor - a competitor".
"I think that getting along with Russian Federation, getting along with China, getting along with others is a good thing, not a bad thing", he added. Well, they could increase it immediately tomorrow and have no problem, ' he said.
"They won't write that", Trump said, pointing at the media.
But in a bid to appease the United States president, they also vow to "submit credible national plans on its implementation".
Though the USA intelligence community and a bipartisan group of senators on the Senate Intelligence Committee both concluded Russian Federation waged a disinformation on Trump's behalf, Trump has indicated he accepts Putin's denials at face value.
"It's also because of your leadership, because your clear message", Stoltenberg responded.