The CEO of Russia's Rostec state corporation said that the company developed "a coating that, like a chameleon, mimics the color of the environment."
"Sadly, it is not being reported that way – the Fake News is going Crazy!" the president tweeted.
"Russia is a foe in certain respects," Trump said.
The Finnish capital is no stranger to high-stakes Moscow-Washington summits.
Trump tried to reassure reporters and NATO leaders at his own post-summit news conference, saying: "I'm very consistent. I'm a very stable genius."
The Republican senator called Trump's performance at NATO "disappointing yet ultimately unsurprising."
Donald Trump's dismal popularity ratings in Europe prompted Steve Bannon and Sean Hannity to work together to help boost the president's image among populist circles.
The president made the claim in an unscheduled press conference Thursday and said he told allies, "I would be very unhappy if they didn't up their commitment very substantially."
The retired four-star general shifted in his seat and looked away as Trump branded Germany a "captive" of Russia, but the White House says he was simply underwhelmed by the catering.
The number of people who think grey cardinals govern steer world affairs has skyrocketed since the start of Russia's fallout with the West.
"We have a tremendous relationship with Germany," Trump said shortly after slamming the U.S. ally.
Trump has said the U.S. should spend less but he spent more on Europe's defense, all for a Russian threat he disputes is there.
"[The strategy] boils down to supporting any, even the wildest ideologies to weaken legitimate governments."
The summit is an opportunity to present an updated strategy for the transatlantic alliance, but President Trump is unlikely to follow the script.
The president said he had a "very good relationship" with embattled British Prime Minister Theresa May.
Trump should not further insult and alienate the Europeans.
"If tomorrow there is an increase in tariffs, like in the car industry, our reaction should be united and strong to show that Europe is a united and sovereign power."
Trump boasted that the NATO leadership is very fond of him, but says Russia must be thinking "if we did like this guy, we made a big mistake."