At the meeting, Trump thanked Estonia, Latvia and Lithuania first and foremost for dedicating two percent of their respective GDPs to defense, reported ETV news broadcast "Aktuaalne kaamera."

Trump stressed that since he took office last January, NATO's budget has increased significantly.

"Since I came in, many, many billions of dollars additional have been paid by countries that weren't paying, and now they're paying," Trump said at the press conference. "And they will have to pay more, frankly. They're going to have to pay more."

According to Kaljulaid, Trump wanted an overview of the Baltics' defense expenditures.

"President Trump wanted a very thorough overview of how much we are spending," Kaljulaid told "Aktuaalne kaamera." "He highlighted the fact that Poland spends significantly more than two percent, and the U.S. even four percent. He hopes that two percent becomes the minimum discussed, and that other European countries spend even more."

The four presidents on Tuesday also adopted a declaration supporting Baltic security which reaffirmed that the U.S. will support the Baltics with $170 million for training, equipment and the purchase of ammunition. The declaration also mentioned air defense.

"We are constantly talking about what could be done to ensure that our defense is credible —  we don't want to overinvest, but we definitely stand for those troops, NATO troops who are currently in the Baltics and Poland, feeling safe," Kaljulaid said. "Air defense is a crucial element."

Trump: I could have a very good relationship with Russia, Putin

Russia was also discussed in connection with Baltic security, although there were initially attempts to avoid the topic at the joint press conference to follow the meeting. ERR Washington correspondent Maria-Ann Rohemäe, however, asked Trump directly how he would handle Russian President Vladimir Putin in light of the Baltics' security concerns.

"It's a real possibility that I could have a good relationship," Trump replied. "And remember this: Getting along with Russia is a good thing. Getting along with China is a good thing. Getting along with other countries, including your three countries, is a good thing, not a bad thing. So I think I could have a very good relationship with Russia and with President Putin. And if I did, that would be a great thing. And there's also a possibility that that won't happen. Who knows?"

The U.S. president also stressed that "There's nobody been tougher on Russia," noting that while Germany and France expelled just four Russian diplomats each in response to the March 4 nerve agent attack in Salisbury, U.K., he expelled 60.