Kim Hjelmgaard

USA TODAY

Babi Yar, the slaughter of 33,771 Jews began 75 years ago Thursday in a valley near Nazi-occupied Kiev — one of the most grim atrocities of the 20th century.

The mass executions of men, women and children took place over 48 hours between Sept. 29-30, 1941.

The people were ordered to strip before they were marched to the Babi Yar ravine and machine-gunned down. The massacre was an early example of how Nazi Germany learned how to commit murder on an unprecedented scale.

Ukraine is marking the massacre's anniversary with a week-long memorial attended by delegations from the United States and Israel.

Ukraine President Petro Poroshenko visited the Babi Yar monument Thursday and tweeted that “we Ukrainians very well understand the grief of the Jews and take it as our own.”

He also spoke about the importance of creating a memorial center dedicated to the victims of the Holocaust in Ukraine, and those killed at Babi Yar.

“The creation of the Babi Yar Holocaust Memorial Center is very significant for the whole of humanity. This center must become a part of the efforts of civilized people to assure the triumph of human values in the research of historical truth,” Poroshenko said.

The center is scheduled to open in 2021, to coincide with the 80th anniversary of Babi Yar.

Israeli President Reuven Rivlin, who cut short his trip to Kiev after the death of his country's statesman, Shimon Peres, addressed Ukraine's parliament on Tuesday.

"The blood of our brothers and sisters that was spilled at that dark time places upon us the duty to remember and teach the whole world about the dangers of not just anti-Semitism, but of all hatred and all racism. While we mourn the past, we must also speak about the present, and look to the future," he said.

Ukrainians, Romani and other non-Jewish groups were also killed at Babi Yar at the hands of Nazis with the help of Ukrainians.

"While Babi Yar was organized by the Nazis, there were willing helpers in the Ukrainian militia," said World Jewish Congress President Ronald Lauder. "This happened all across Europe. In almost every occupied country, local people helped the Germans round up their Jews. In some cases, the locals were even more enthusiastic in their killing than the Nazis. And that is what happened at Babi Yar."

Up to 6 million Jews — approximately two-thirds of the Jews in Europe — were murdered during the Holocaust.

Millions of non-Jewish people were also exterminated, including communists, homosexuals, resistance fighters and people with physical and mental disabilities.