Poland deaths not caused by Russian attack, Nato says

"We have no indications Russia is planning offensive military action against Nato allies," he added.

The incident "hasn't changed our fundamental assessment of the [Russian] threat against Nato allies," he also said.

Stoltenberg spoke following an emergency meeting of Nato ambassadors in Brussels, called after the war claimed its first victims on allied territory on Tuesday— two Poles at a grain storage site in Przewodów, a village in eastern Poland near the Ukraine border.

Polish president Andrzej Duda also said in Warsaw on Wednesday: "From the information that we and our allies have, it was an S-300 rocket made in the Soviet Union, an old rocket, and there is no evidence that it was launched by the Russian side."

"It is highly probable that it was fired by Ukrainian anti-aircraft defence," he added.

Initial remarks by some EU and Ukrainian ministers had blamed the deaths on a Russian rocket, prompting feverish talk in media and social media of a potential Nato-Russia clash.

Nato's investigation into exactly what happened was still "ongoing", Stoltenberg said.

But he reiterated that even if a Ukrainian missile had hit Przewodów by accident, Russia was still morally to blame.

"It's not Ukraine's fault," Stoltenberg said several times on Wednesday.

"Russia bears the ultimate responsibility for what happened in Poland yesterday. This is a direct result of the ongoing war and wave of Russian [cruise missile] attacks against Ukraine yesterday. Of course, Ukraine has a right to shoot down those missiles," he said.

Poland and Nato allies would "continue to support Ukraine in its right to self-defence," he added, amid a new arms-delivery pledge by Sweden.

"Our top priority now is to provide air-defence systems to Ukraine," Stoltenberg said.

Tuesday's blast in Poland came after more than 100 Russian missiles and drones rained down the same day on Ukraine, where 6,500 civilians have been killed by Russian fire since February, according to UN figures.

Russian president Vladimir Putin was trying to break Ukrainian morale, Kostiantyn Yelisieiev, Ukraine's former EU ambassador, told EUobserver from Kyiv.

But "the mood here is opposite", he said.

"The more Putin tries to make Ukraine capitulate, the more motivation to resist it brings," he said.

Putin "knows he's losing," Yelisieiev said, following recent victories by the Ukrainian army on the ground in east Ukraine.

"I don't know how anybody around the world could ever shake his [Putin's] hand again, given Russia's style of warfare against Ukraine," the Ukrainian diplomat, who has taken up arms against the Russian invasion, added.

Propaganda value

The likely fact a Ukrainian shell hit Poland is a gift for Russian propaganda, which has long tried to stir anti-Ukrainian feeling in Polish society.

But at the same time, Nato's candour on the painful truth disarmed Russian info-war allegations that the West was trying to orchestrate a conflict with Russia.

"We're prepared to handle situations like this in a firm, calm, resolute way, but also in a way that prevents further escalation," Stoltenberg said.

"Nato allies reacted in a prudent and responsible way," he said, referring to how Nato leaders handled the flurry of initial anti-Russian allegations on Tuesday.

"We are preparing for incidents like this ... to prevent them from spiralling out of control," he added.

Tuesday's deaths saw leaders from around Europe voice solidarity with Poland.

The Polish government initially considered asking Nato to invoke Article 4 of its treaty — emergency high-level talks on a clear and present danger — but later changed its mind, downgrading the crisis.

Stoltenberg said Nato was ready to "very quickly" move extra air-defence planes and ships into the region to help allies, if the situation changed.

But both he and Germany ruled out a Nato-imposed no-fly zone over western Ukraine, given that this would make Nato a party to the war, if it fired at Russian jets or air-defence systems on the ground to do the job.