WARSAW, Poland — Holocaust survivors, politicians, religious leaders and others marked International Holocaust Remembrance Day on Sunday with solemn prayers and the now oft-repeated warnings to never let such horrors happen again.Events took place at sites including Auschwitz-Birkenau, the former death camp where Hitler's Germany killed at least 1.1 million people, mostly Jews, in southern Poland. In Warsaw, prayers were also held at a monument to the fighters of the Warsaw Ghetto Uprising of 1943.Pope Benedict XVI, speaking from his window at St. Peter's Square at the Vatican, warned that humanity must always be on guard against a repeat of murderous racism."The memory of this immense tragedy, which above all struck so harshly the Jewish people, must represent for everyone a constant warning so that the horrors of the past are not repeated, so that every form of hatred and racism is overcome, and that respect for, and dignity of, every human person is encouraged," the German-born pontiff said.Not all words spoken by dignitaries struck the right tone, however.On the sidelines of a ceremony in Milan, former Italian Premier Silvio Berlusconi sparked outrage when he praised Benito Mussolini for "having done good" despite the Fascist dictator's anti-Jewish laws. Berlusconi also defended Mussolini for allying himself with Hitler, saying he likely reasoned that it would be better to be on the winning side.The United Nations in 2005 designated Jan. 27 as a yearly memorial day for the victims of the Holocaust — 6 million Jews and millions of other victims of Nazi Germany during World War II. The day was chosen because it falls on the anniversary of the liberation in 1945 of Auschwitz, the Nazis' most notorious death camp and a symbol of the evil inflicted across the continent."Those who experienced the horrors of the cattle cars, ghettos, and concentration camps have witnessed humanity at its very worst and know too well the pain of losing loved ones to senseless violence," U.S. President Barack Obama said in a statement.Obama went on to say that like those who resisted the Nazis, "we must commit ourselves to resisting hate and persecution in all its forms. The United States, along with the international community, resolves to stand in the way of any tyrant or dictator who commits crimes against humanity, and stay true to the principle of 'Never Again.'"As every year, Holocaust survivors gathered in the cold Polish winter at Auschwitz — but they shrink in number each year.This year the key event in the ceremonies was the opening of an exhibition prepared by Russian experts that depicts Soviet suffering at the camp and the Soviet role in liberating it. The opening was presided over by Sergey Naryshkin, chairman of the Russian State Duma.Several years ago, Polish officials stopped the opening of a previous exhibition. It was deemed offensive because the Russians depicted Poles, Lithuanians and others in Soviet-controlled territory as Soviet citizens. Poles and others protested this label since they were occupied against their will by the Soviets at the start of World War II.The new exhibition — titled "Tragedy. Courage. Liberation" and prepared by the Museum of the Great Patriotic War in Moscow — removes the controversial terminology. It took years of discussions between Polish and Russian experts to finally complete it.The exhibition narrates the Nazi crimes committed against Soviet POWS at Auschwitz, where they were the fourth largest group of prisoners, and at other sites. And it shows how the Red Army liberated the camp on Jan. 27, 1945, and helped the inmates afterward.Also Sunday, a ceremony was held in Moscow at the Jewish Museum and Tolerance Center, which opened in November and is Russia's first major attempt to tell the story of its Jewish community. The museum portrays Russia as a safe and welcoming place for Jews today despite its history of pogroms and discrimination.In Serbia, survivors and officials gathered at the site of a former concentration camp in the capital, Belgrade, to remember the Jewish, Serb and Roma victims of the Nazi occupation of the country.Parliament speaker Nebojsa Stefanovic said it is the task of the new generations never to forget the Holocaust crimes, including those against Serbs."Many brutal crimes have been left without punishment, redemption and commemoration," he said. "I want to believe that by remembering the death and suffering of the victims the new generations will be obliged to fight any form of prejudice, racism and chauvinism, anti-Semitism and hatred."___Associated Press writers Frances D'Emilio in Rome, Jovana Gec in Belgrade and Lynn Berry in Moscow contributed to this report.