Poland's Prime Minister Donald warned on Monday that the war in eastern Ukraine risks spreading if NATO does not toughen its stance quickly.

Tusk, tipped as the European Union's next president, claimed that "our Western community is threatened by war, not just in eastern Ukraine", as Poles marked 75 years since the outbreak of World War II.

"There is still time to stop those for whom violence, force and aggression have again become part of their political arsenal," Tusk said in a clear reference to Moscow's role in the Ukraine crisis during ceremonies to mark Nazi Germany's attack on Poland on September 1, 1939.

He said this week's NATO's summit must come up with a new security policy to ensure that the declaration "'Never again war' cannot be a manifesto of weakness and helpless".

Tusk insisted that in trying to avoid war there "cannot be an illusion that there are no people and countries around us that would like to use might and war in running their policy.

"Observing the tragedy in Ukraine, the war -- because this is what it must be termed -- we know that September 1939 can never be repeated," he added.

Tusk has been one of European Union's most outspoken leaders on the Ukraine crisis and has readily questioned Russia's role in provoking it.

He and other senior officials in the region have repeatedly urged NATO to be serious about reinforcing its eastern flank amid growing fears in ex-communist Poland and the three formerly Soviet Baltic states over a resurgent Russia.

The 28-member bloc named Tusk its new president this weekend and he will take over from Herman van Rompuy on December 1 as chair of EU and eurozone summits.

Polish intellectuals echoed Tusk Monday, insisting there are parallels between the appeasement of Nazi Germany prior to WWII and Europe's current predicament.

- 'Myopic' appeasement -

And they lambasted France in particular for its "myopic" decision to continue to sell warships to Russia.

"French President Francois Hollande and his government intend to take a step that is more harmful than the passivity of France in 1939," said the statement signed by Oscar-winning film director winner Andrzej Wajda and former Polish foreign minister Wladyslaw Bartoszewski, an Auschwitz survivor, among others.

"They are the only ones in Europe who want to back the aggressor by selling it big new Mistral warships," they added.

"This kind of selfish and myopic European policy towards the aggressor must never be repeated. Yet Ukraine's predicament is reminiscent of 1939: an aggressive Russia annexed Crimea, part of its smaller neighbour," the statement said.

"Whoever engages in a policy of 'business as usual', risks the death of hundreds of thousands of Ukrainians and Russians, hundreds of thousands of refugees and further attacks by Putin's imperialism on other countries," they added.