An air-raid siren brought rush-hour traffic to a two-minute standstill and Holocaust survivors laid wreaths on memorials Thursday as Israel mourned the 6 million Jews killed in World War II.

Flags flew at half-staff and many shops were closed across the nation for Holocaust Day, a day commemorated each year exactly one week before Independence Day.

In Jerusalem, hundreds of survivors, soldiers and schoolchildren packed the plaza at Israel's Holocaust memorial and archive, Yad Vashem, for a wreath-laying ceremony at a statue commemorating the Warsaw Ghetto uprising.