Finnish President Sauli Niinistö said the deadly explosion in Poland near the Ukrainian border does not appear to have been fired from Russian territory, referring to flight trajectories.
Noting that it is important to exactly pinpoint the source of the blast that claimed the lives of two people on Tuesday evening, Niinistö added that people commenting about the incident should remain cool-headed.
He said the events in Poland showed that war is a harsh situation in which unintended things happen.
Meanwhile, Nato's Secretary General, Jens Stoltenberg, said the explosion in Poland was likely caused by a Russian-made S-300 missile used in Ukrainian air defence. The missiles have a range of about 200 kilometres, indicating that it could not have been fired from Russia.
Speaking at a press briefing, Stoltenberg said the blast was not a deliberate attack, adding that it was not Ukraine's fault, as Russia is illegally attacking Ukraine.
Ahead of Stoltenberg's announcement, Polish President Andrzej Duda suggested that there were no signs that the rocket strike was intentional, according to news service Reuters.
"We have no evidence that the rocket was launched by the Russian side, there is a high probability that the rocket was used by the Ukrainian defence forces," Duda said.
Poland was continuing to look into possibly invoking Nato Article 4 on Wednesday, however the country's Prime Minister, Mateusz Morawiecki, said the measure might not be necessary.
Ambassadors of Nato are holding an emergency meeting about the incident. Finland and Sweden, which are still awaiting approval of their membership in the alliance, were attending the meeting as observers.
Would you like a roundup of the week's top stories in your inbox every Thursday? Then sign up to receive our weekly email!
