(CNN) Germany's President Frank-Walter Steinmeier has asked for Poland's forgiveness 80 years after the start of World War II.

"I stand before you, those who have survived, before the descendants of the victims, the old and the young residents of Wielun, I am humbled and grateful," Steinmeier said during a ceremony in the Polish city of Wielun, the site of one of the first Nazi bombings in the country on September 1, 1939.

"I bow to the victims of the attack in Wielun, I pay tribute to the Polish victims of German tyranny and I ask for forgiveness," he said.

Nearly 6 million Poles died during World War II , which remains the bloodiest conflict in history.

More than 50 million people were killed in the conflict overall, including some 6 million Jews, half of whom were Polish.

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