While the United States and Europe have historically been close military and economic allies, President Donald Trump has upended that order by repeatedly taking Europe to task over defense spending and trade while pursuing a closer U.S. relationship with adversary Russian President Vladimir Putin.
"I think it's very sad when Germany makes a massive oil and gas deal with Russia, where you're supposed to be guarding against Russia, and Germany goes out and pays billions and billions of dollars a year to Russia", Trump told Stoltenberg.
The president appeared to be referring to the Nord Stream 2 pipeline that would double the amount of gas Russian Federation can send directly to Germany, skirting transit countries such as Ukraine.
German Defense Minister Ursula von der Leyen dismissed Trump's comments, saying Germany is not captive to Russian Federation and the country can take Trump's criticisms in stride.
Canada only contributed 1.29% of its GDP, while Germany - which has drawn criticism from President Trump - spent 1.24% of its GDP on defense previous year.
Mr Trump dominated the day and is set to stay in the spotlight as he visits the United Kingdom and prepares for a summit with Russian president Vladimir Putin.
The remarks, which came during his first engagement at the two-day gathering, reflect Mr Trump's anger that so few countries are meeting Nato's 2 per cent defence spending target.
House Speaker Paul Ryan told reporters on Capitol Hill that "NATO is indispensable".
"I wanted to say that, because of current events, I have witnessed this myself, that a part of Germany was controlled by the Soviet Union".
"I am pleased to have this opportunity to be here for this exchange of views", she said, through a translator. Members have pledged to get to 2 percent, but most countries are well off the mark - something Trump campaigned to change.
By accusing a global rival of having unsavory ties with Russia-at the moment investigators are looking into the president's own unsavory ties with Russia-Trump is continuing his use of the so-called "boomerang insult", a strategy that seeks to deflects attacks against him on to his critics.