Israel's president Shimon Peres and Prime Minister Benjamin Netanyahu have both called on the world to learn the lessons of the Holocaust and stop Iran from acquiring atomic weapons. They made the appeal at the opening of the annual memorial day for the six million Jews killed in the Holocaust.

Visitors look at pictures of Jews killed in the Holocaust during a visit to the Hall of Names at Yad Vashem's Holocaust History Museum in Jerusalem April 18, 2012.

In the presence of hundreds of Holocaust survivors and their families, Peres recalled how Nazi troops beat members of his extended family and ordered them to march toward the town's synagogue.

Netanyahu warned of the danger posed by Iran and Israel's moral obligation to prevent it from acquiring a nuclear weapon. The annual remembrance is one of the most solemn in Israel's calendar.

Restaurants, cafes and places of entertainment are shut down, and media are dedicated almost exclusively to the Holocaust. On Thursday morning, Israel will come to a standstill with a two-minute siren heard across the country.