Leaders and officials from across Europe and the United States gathered in Gdansk of northern Poland on Tuesday to mark the 70th anniversary of the outbreak of the European war in World War Two.

Soldiers stand guard by the monument of World War Two at Westerplatte, outside of Gdansk September 1, 2009. European leaders will commemorate on Tuesday the 70th anniversary of the outbreak of World War Two at ceremonies in Poland. [Agencies]

Russian Prime Minister Vladimir Putin, German Chancellor Angela Merkel were among the politicians from about 20 European countries and the United States, who participated in the ceremonies in Westerplatte, by the port of Gdansk, on Tuesday.

"Today marks the 70th anniversary of the outbreak of the most terrible of wars. We are in Westerplatte, the symbol of heroic resistance against the stronger enemy," Poland's President Lech Kaczynski said while opening the international part of the ceremonies.

The shelling of Westerplatte by the German Schleswig-Holstein warship started at 4:45 a.m. on Sept. 1, 1939 and was long considered to have been the first episode in the Nazi aggression on Poland that started the World War in Europe.

Poland's Prime Minister Donald Tusk said during the Westerplatte ceremonies that the "biggest tragedy in the history of the humankind began in Gdansk on Sept. 1."

"Why am I speaking about those examples of war cruelties? Because we are all deeply convinced that the memory about those atrocities, about genocide, is perhaps the most important, and the most effective shield against the threat of the next war," Tusk said.

Poland's Prime Minister Donald Tusk makes a speech by the monument of World War Two at Westerplatte, outside of Gdansk September 1, 2009. [Agencies]

"I bow my head before WWII victims, it is our duty to accept responsibility for what had happened (then)," said German Chancellor Merkel in her speech delivered during the observances.

Evil done during the war could not be reversed and "scars will be forever visible," she said. "Here in Westerplatte I recall the fate of the Poles who suffered under criminal German occupation, I recall the Holocaust of European Jews, I recall people who died a terrible death in German death camps, and millions who fell in struggle against the German occupation," Merkel said.

Poland and Germany have covered a very long road since 1939, she said. "We now have very friendly relations on many planes between our two countries."

"We have gathered where the first shots of the most bloody war in human history were fired in order to pay tribute to dozens of millions of its victims: soldiers, civilians, people of various nationalities, religions and beliefs," Russian Prime Minister Putin said in his address at Westerplatte.