He said his nation might consider joining NATO if it felt threatened.

Finnish President Sauli Niinistö said Sunday that he’s recently seen changes in Russian President Vladimir Putin’s behavior, saying that he now sounds more “decisive” than in the past.

Niinistö, who has been in close contact with Putin, recalled an exchange the two shared on the phone. During one of the regular calls, Niinistö said he pushed back against Putin by standing up for his country’s sovereignty. That is when Putin switched tones, he said, then began to “officially” read his list of demands.

“That was a change in his behavior, and I want to guess, and from that I guess that he wants to be very decisive, wants to sound like one. It was a different kind of behavior,” he said during an interview on CNN’s “State of the Union.”

For decades, Finland has kept a delicate balance in its relationship with Russia, having been invaded by the Soviet Union in 1939. The country, which borders Russia, stayed scrupulously neutral throughout the Cold War, becoming neither part of the Warsaw Pact nor of NATO.

That delicate balance, however, might be tipped if Russia were to invade Ukraine, which President Joe Biden and others throughout the West have painted as an imminent threat. While Niinistö emphasized his country wasn’t planning on a dramatic change in its relationship with Russia, he suggested Russia’s actions are making Finnish people rethink joining NATO.

“A lot depends, also, what actually happens in Ukraine and how Russia is going to behave after that,” he said. “If Russia sees a success story for them, that makes them more dangerous.”

However, he emphasized that Finland doesn’t feel threatened by Russia as of now.

“Finland is a stable democracy. We are a member of the European Union and part of the West,” he said. “We are not afraid of Russian tanks suddenly crossing the Finnish border.”