Several heads of state, including French President Francois Hollande, German President Joachim Gauck and Ukrainian President Petro Poroshenko were among a host of leaders to attend Tuesday's service in a large white tent at the entry to the camp.
Russia, the United States and Israel sent lower-ranking representatives.
Before leaving for Poland, Hollande echoed warnings by German Chancellor Angela Merkel and Hollywood mogul Steven Spielberg over violence against Jews in modern-day Europe.
"France is your homeland," Hollande told Jews in Paris, describing as "unbearable" the rise in anti-Semitic attacks in France, underscored by the Islamist killing of four people at a kosher supermarket in Paris earlier this month.
Anti-Semitic acts in France, home to Europe's largest Jewish population, doubled in 2014 to 851 from the previous year, France's main Jewish group CRIF said Tuesday.
A new exodus?
European Jewish Congress chief Moshe Kantor warned that Europe was "close to" a new exodus of Jews, saying "jihadism is very close to Nazism".
At an event Monday, January 26, in Berlin to mark the liberation of Auschwitz, Merkel said it was a "disgrace" that Jews in Germany faced insults or threats because of their Jewishness or support for Israel.
US President Barack Obama pledged Tuesday "never to forget" those murdered by the Nazi regime and also voiced concerns over anti-Semitism.
Asked whether he thought the world had learnt the lesson of the Holocaust and other mass killings since, from the 1994 Rwandan genocide to the ongoing civil war in Syria, David Wisnia, Auschwitz prisoner number 83,526 replied: "No we have not!"
Through propaganda, people anywhere could still be incited to kill others simply "because they believe different things than you do, or their colour is different than yours or they speak a different language", he said.
Part of Adolf Hitler's genocide plan against European Jews, dubbed the "Final Solution", Auschwitz-Birkenau operated in the occupied southern Polish town of Oswiecim between June 1940 and January 1945.
Allies knew in 1942
Of the more than 1.3 million people held there, some 1.1 million mostly Jewish prisoners perished, either in the gas chambers or by starvation or disease.
Historians estimate that up to 150,000 ethnic Poles were also held at Auschwitz. Used as slave laborers, half died at the camp.
European Roma were also targeted for annihilation. Around 23,000 were deported to Auschwitz, of whom only 2,000 survived, according to estimates.
The Nazis killed 6 million of pre-war Europe's 11 million Jews and more than half of its roughly one million Roma. Black Germans, homosexuals, Jehovah's Witnesses and the mentally and physically disabled were also persecuted as "undesirables".
Historical records show that by 1942, the Polish resistance provided Allied powers with eyewitness accounts of the Holocaust. But inexplicably, Washington and London failed to act against the six death camps the Nazis set up in occupied Poland.
"The debate as to why the Allies did not bomb the supply lines to Auschwitz remains unresolved," survivor Marcel Tuchman told Agence France-Presse.
"Whether there was a sinister reason behind it or whether it was just tactical, in that they didn't want to divert their air force remains unclear," the 93-year-old said.
"A little bomb in the proper place would have really helped." – Rappler.com