Plans for a new gas pipeline that would bypass Ukraine, the Nord Stream 2, have been in the works for years, but the project remains controversial.
"Trump at NATO Summit: It's not just bad, it's a catastrophe", the influential Sueddeutsche Zeitung headlined its story online.
Baltic leaders, fearful of any repeat of Russia's annexation of Crimea, called for unity, while Slovak President Andre Kiska said his country was "one of the good guys" because it was increasing defence spending. Germany is the largest economy in the EU.
Alluding to Trump's comments about Germany, Kerry also said that "European energy security is an important topic for allies to discuss, even when they disagree".
Though the insult will hardly engender warmth from German chancellor Angela Merkel, who Trump is due to meet later today, German defense minister Ursula von der Leyen seemed relatively unperturbed.
"We're protecting Germany, we're protecting France, we're protecting all of these countries".
Canada signed on to an agreement to move "toward" the two per cent spending target at the 2014 North Atlantic Treaty Organisation summit in Wales - a commitment that would cost Canadian taxpayers billions of dollars - to satisfy US and North Atlantic Treaty Organisation demands.
Trump's pipeline criticism was an unusual line of attack for a president who has proclaimed himself eager to improve relations with Russia's Vladimir Putin and dismissed the USA intelligence community's assessment that Russian Federation tried to undermine Western democracy by meddling in the 2016 US presidential election to help Trump win.
During a breakfast with NATO Secretary General Jens Stoltenberg, Trump accused Germany of being "a captive of Russia" because of Berlin's energy deals with Moscow. So you tell me, is that appropriate?
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.
He said: "Why are their (sic) only 5 out of 29 countries that have met their commitment? I think it's very unfair to our country".
During a working breakfast that marked the start of the summit, Trump claimed Germany is "controlled" by Russian Federation due to an energy partnership between the two countries.
Trump's comments were a remarkable criticism for a United States president to make about a close USA ally and is likely to increase tensions between the U.S. and its European allies. Smith listed several ways that Germany has demonstrated friendship to the USA, including treating wounded American soldiers amid conflicts with terrorist groups.
How did leaders respond to Trump's tirade?
TRUMP: "We're protecting Germany". The pipeline, set to become operational in 2019-2020, will run from Russian Federation to Germany (Ust-Luga to Greifswald) and double the pipeline capacity between the two nations.