Ukraine is marking the 65th anniversary of the Babi Yar massacre, when more than 30,000 Jews were shot by the Nazis in Kiev during World War II.
Almost 34,000 Jews were killed in Babi Yar in September 1941
Israeli President Moshe Katzav is among dignitaries from more than 40 nations attending the two-day commemorations.
The killings began 10 days after Nazi troops occupied Ukraine's capital. The massacre lasted for two days.
During the war, at least 100,000 people - including Gypsies and Soviet Army prisoners - were killed in Babi Yar.
In September 1941, the Jewish residents of the then capital of Soviet Ukraine were ordered to gather near a cemetery on the edge of the city.
Many thought they were being deported, but instead they were told to undress and walk to the edge of the Babi Yar ravine.
Over the next 48 hours almost 34,000 people were shot dead.
The massacre is being remembered with a series of events which started on Tuesday.
The commemorations were initiated by Ukrainian President Viktor Yushchenko, whose father was imprisoned at the Auschwitz concentration camp during the war.
"Babi Yar is a symbol ... of the most secret Holocaust," said Moshe Kantor, founder of the World Holocaust Forum, which helped organise the events.
"The majority of the population doesn't know that after the Babi Yar killings happened, there were 6,000 more Babi Yars. We have to know about this," he said.
In Soviet times there were no high profile ceremonies to officially mark the massacre.
It was only in the early 1990s, after the collapse of the USSR, that a monument was put up to remember the Jewish victims.