Finnish President Sauli Niinistö said President Vladimir Putin's decision to declare a partial mobilisation of Russian operations in Ukraine is an indication of the country's poorly-run military operations.
"The war of aggression has not produced results, so they need to invest more," Niinistö said.
He made the comments at a press conference on Wednesday in New York City, where he is leading the Finnish delegation at the UN General Assembly.
In a statement earlier in the day, Putin also warned the West that he wasn't bluffing when he said he was prepared to use nuclear weapons to defend Russia.
Reacting to a question about whether Russia would actually resort to the use of nuclear weapons, Niinistö said on one hand he does not believe it would, but added that the question remained up in the air.
"With some knowledge of how Putin thinks and reasons, I can say that he is not one to concede defeat. That makes this an unpredictable situation," Niinistö said.
Niinistö also said that he does not think Finland will be required to request military assistance from the US, for example, in terms of defending itself against Russia.
"Looking at the near future and a little beyond that, Russia is completely tied to Ukraine," Niinistö said.
He added that Finland's security has already been bolstered by the US and most other Nato countries' ratification of Finland's and Sweden's accession to Nato.
On Thursday, Niinistö is headed to Washington DC for yet-to-be-specified bilateral meetings.
Edited to clarify Russia declared a partial mobilisation of Russian operations.