Gdansk -- German leader Angela Merkel recalled World War II as the "most tragic chapter" in European history Tuesday as the continent marked 70 years since the conflict began on the shores of the Baltic.

In a ceremony also attended by veterans of the 1939-45 war, Merkel joined leaders from countries including Poland and Russia at the former naval base which was the site of the first battle of the war on September 1, 1939.

But while the ceremony underlined how Europe has been able to heal its divisions in the intervening years, old wounds were clear to see with fresh disputes over its historical legacy.

"Seventy years ago today the German invasion of Poland opened up the most tragic chapter in European history," said Merkel.

"The war unleashed by Germany resulted in immeasurable suffering to many peoples -- years of deprivation of rights, of humiliation and destruction."

The Polish army, outnumbered by more than two to one, surrendered a little over a month after the battle on Gdansk's Westerplatte peninsula and a brutal Nazi occupation began.

Almost six million Polish citizens perished in the war, half of them Jewish.

Before heading to Poland, Merkel had said on German television that her country bore full responsibility for the conflict.

"Germany attacked Poland, Germany started World War II. We caused unending suffering in the world. Sixty million dead ... was the result," the German chancellor said.

Speaking at a pre-dawn ceremony before Merkel's arrival, Polish Prime Minister Donald Tusk also underlined how the memories and bitterness of 70 years ago still burned.

"We are here to remember who in that war was the aggressor and who was the victim, for without an honest memory neither Europe, nor Poland, nor the world will ever live in security," said Tusk.

Bogdan Kolodziejski, who was 10 when the war began and became a resistance courier, remembered the start of the occupation as he gathered in Gdansk to pay his respects.

"I've never forgotten the day the Germans marched into Warsaw, singing at the top of their voices," he told AFP.

Many Poles still habour bitterness towards Russia over the Molotov-Ribbentrop pact of August 1939 under which Germany and the Soviet Union secretly agreed to carve up Poland between them at the start of the war.

In his address, Russian Prime Minister Vladimir Putin acknowledged the pact had been a mistake but said all attempts to appease the Nazis were "morally unacceptable" -- an apparent reference to the 1938 Munich agreement in which Britain and France told Adolf Hitler they would not object to the annexation of parts of the former Czechoslovakia.

"All attempts to appease the Nazis between 1934 and 1939 through various agreements and pacts were morally unacceptable and politically senseless, harmful and dangerous," Putin said.

"We must admit these mistakes. Our country has done this. The Russian parliament has condemned the Molotov-Ribbentrop Pact. We have a right to expect this from other countries that also agreed deals with the Nazis."

Britain and France, bound to Poland by military pacts, declared war on Germany on September 3, 1939, each pulling their vast empires into the conflict.

For Russia, what is known as the "Great Patriotic War" started on June 22, 1941, when the Nazis tore up their non-aggression pact and invaded.

Suddenly the Soviet forces, from having been the occupiers of part of Poland, found themselves fighting against a common enemy.

Around 8.6 million Soviet soldiers and 27-28 million civilians were killed in the war, which ended with Germany's crushing defeat in 1945.

Merkel said that the continent's recovery since then should be a source of pride.

"Europe ... has transformed itself from a continent of terror and violence into a continent of freedom and peace. That this was possible is nothing more and nothing less than a wonder," she said.

AFP/Expatica