JERUSALEM - Sirens pierced the air in a mournful two-minute wail throughout Israel on Thursday in a tribute to the six million Jews murdered by the Nazis as the country marked Holocaust remembrance day.

In an annual ritual, drivers switched off their engines and people put aside their daily activities to stand at attention as the sirens sounded.

Theaters and other places of entertainment shut down Wednesday night, when the observances officially began. Radio and television programming focused exclusively on the Holocaust, and melancholy music poured over the airwaves.

In a speech Wednesday evening marking remembrance day, Israel's president took a veiled swipe at Iran and its disputed nuclear program.

Shimon Peres charged that the world woke up too late to eliminate the threat of Adolf Hitler before he started a war that killed 60 million people. He warned that the world must not let that happen again. "In history, it is forbidden to be late," he said at the ceremony at Yad Vashem, Israel's official Holocaust memorial.

Although Peres did not refer specifically to either Iran or its president his aides said later that he was alluding to them when he talked about Hitler and the Nazi regime in Germany.

Despite Iranian insistence its nuclear program is peaceful, Israel, the U.S. and others believe Iran is trying to build atomic weapons. Iranian President Mahmoud Ahmadinejad has called repeatedly for the Jewish state's destruction.

About 270,000 Holocaust survivors live in Israel, of whom about 80,000 survived Nazi death camps, according to Zeev Factor, chairman of a commission working on benefits for them.