Former enemies and allies somberly marked the 70th anniversary of the start of World War II on Tuesday, underlining the need to remember the bloodiest conflict in the 20th century so as not to repeat it.
Russian Prime Minister Vladimir Putin, whose country sided with Nazi Germany during the initial invasion of Poland in 1939, said the war and its causes needed to be studied from all perspectives.
"We should examine everything which ended up bringing about the tragedy of Sept. 1, 1939," Putin said, standing next to Poland's Prime Minister Donald Tusk after the two met ahead of official commemorations. "We must do this so that this tragedy never happens again."
Poland's leaders gathered at dawn on Gdansk's Westerplatte peninsula to mark the exact time the German battleship Schleswig-Holstein, in the war's opening salvo, shelled a tiny Polish military outpost housing the navy's arsenal.
Red-and-white Polish flags fluttered as the officials opened the ceremony at 4:45 a.m. local time, placing wreaths at the foot of the monument to the defenders of Westerplatte. An honor guard looked on.
"Westerplatte is a symbol, a symbol of the heroic fight of the weaker against the stronger," President Lech Kaczynski said. "It is proof of patriotism and an unbreakable spirit. Glory to the heroes of those days, glory to the heroes of Westerplatte, glory to all of the soldiers who fought in World War II against German Nazism, and against Bolshevik totalitarianism."
Tusk warned of the dangers of forgetting the war's lessons.
"We meet here to remember who started the war, who the culprit was, who the executioner in the war was, and who was the victim of this aggression," Tusk said.
"We meet here to remember this, because we Poles know that, without this memory — honest memory about the truth, about the sources of World War II — Poland, Europe and the world will not be safe," he said.
The initial German attack on Poland started more than five years of war that would engulf the world and result in the slaughter of more than 50 million people as the German war machine rolled over Europe.
Poland alone lost 6 million citizens, half of them Jews. During the German occupation, the country was used as a base for the Nazis' genocide machinery. It was home to Auschwitz, Majdanek, Sobibor and other death camps built for the annihilation of Europe's Jews.
At the height of the war, the European theater stretched from North Africa to the outskirts of Moscow, and pitted Germany and its allies, including Italy, against Britain, France, the Soviet Union and the United States, along with a host of other countries, including Polish forces in exile.
The war in Europe ended May 8, 1945, with Germany's unconditional surrender.
President Barack Obama, who was not at Tuesday's ceremonies, sent a message noting that today, as a NATO member, Poland is protected by a creed that says an attack on one is an attack on all.
"We celebrate together the determination of the people of Poland to fight authoritarianism and to choose democracy and freedom," Obama said in the message to Poland. "Today, we live in a different era in which the United States and Poland are close allies, partners in meeting global challenges to our security and prosperity, and in supporting fundamental human rights around the world."
Earlier Tuesday, German Chancellor Angela Merkel, who was taking part in the commemoration, told Germany's ARD television that her country would never forget the "causes and effects" of the war.
"Germany triggered the Second World War," she said. "We brought endless suffering to the world."
Within a month of the Sept. 1 attack, Poland was overwhelmed by the Nazi blitzkrieg from the west, and an attack two weeks later from the east by the Soviet Union, which had signed a pact with Hitler's Germany.
Putin downplayed Russia's responsibility, however, saying that other countries had also negotiated with Nazi Germany before the war broke out. He emphasized instead the Soviet Union's role in fighting the Nazis.
"Today is a special day ... the day of the beginning of the second world war during which Russians and Poles together were fighting against one enemy, the Nazis," Putin said.
Tusk acknowledged the Red Army's defeat of the Nazis in Poland and vowed his nation and Russia would investigate the "painful elements of our common history."
"If, in the past, it was possible for the Poles and the Germans and the Russians and the Germans, for God's sake, why isn't it possible for the Poles and the Russians?" he said. "This meeting today ... is another step in building the fair foundations for an increasingly good dialogue."
About 20 European leaders and officials, including French Premier Francois Fillon and British Foreign Secretary David Miliband, were joining Merkel and Putin for the ceremonies.
The U.S. was being represented by National Security Adviser James Jones. The delegation, which is lower-ranking than that of most European nations, has disappointed some in Poland who view Washington as a historical ally.
U.S. State Department spokesman Ian Kelly said the delegation was no indication of a chill in relations between the two nations.
"There are very deep and extensive ties between the U.S. and Poland," Kelly said. "We appreciate the, the tremendous sacrifice that the people of Poland made in World War II."