Tel Aviv - Sirens sounded across Israel for two minutes Tuesday morning, as Israelis stood in solemn silence to remember the victims of the Nazi World War II genocide.

As the sirens sounded at 10 am (0800 GMT), traffic came to a total standstill. Drivers stood next to their cars and pedestrians stopped walking, many of them standing to attention or with their heads bowed.

Holocaust Memorial Day began Monday night with a ceremony at Jerusalem's Yad Vashem Holocaust Memorial Institute, attended by state leaders, foreign diplomats, and Holocaust survivors and their relatives.

Six survivors lit six beacons honouring the 6 million Jews killed by the Nazis and their collaborators.

Israeli Prime Minister Benjamin Netanyahu used the ceremony to condemn Iranian President Mahmoud Ahmadinejad for denying the Holocaust, and to warn that hatred toward Jews, and Israel, remained strong.

"The sad fact is that is that at a time we are marking the events of the Holocaust, here at Yad Vashem, in Jerusalem, there are those who choose to participate in a display of hatred against Israel which is being held at these very hours in the heart of Europe.

"From here I turn to you, the president of Switzerland, and ask you - how can you as the head of an enlightened state, meet with someone who denies the Holocaust and wishes for another Holocaust?"

Netanyahu also listed and thanked those countries who boycotted and walked out of the UN anti-racism conference taking place in Geneva. Israel says the conference's agenda singles it out, while paying less attention to grave human rights abuses elsewhere in the world.

Commemorations continue Tuesday with ceremonies at Yad Vashem and television and radio channels broadcasting special programmes focusing on the Nazi attempt to murder the Jews of Europe.

The United Nations has designated January 27, the day the Auschwitz death camp was liberated in 1945, as international Holocaust remembrance day, but Israel has traditionally marked it on the 27th day of the Jewish month of Nissan - one week before Independence Day to symbolize the birth of the Jewish state from the ashes of the Holocaust.

According to counts held before and after the war, two thirds of Europe's 9 million Jews perished at the hands of the Nazis and their collaborators.