PARIS, France - The World War II extermination of Jews by Nazi Germany began after the invasion of Poland in 1939 and increased in scale with the creation of death camps.

The Nazis called it the "Final Solution to the Jewish Question" and killed six million Jews -- more than a third of the world's Jewish population at the time.

STARVATION, DEATH SQUADS

The first massacres were perpetrated through starvation and mass shootings.

In Poland, Jews were imprisoned in ghettos from 1939 to late 1941 where many starved to death or died of disease.

The Nazi government also despatched mobile death squads called Einsatzgruppen which mowed down one million people in what is known as the "Holocaust by bullets".

They were mainly Jews and Soviet prisoners of war in Polish, Baltic and Soviet territories.

GAS CHAMBERS

Leader of the Nazi paramilitary SS, Heinrich Himmler, and his deputy Reinhard Heydrich established extermination through gas chambers in 1941, a technique that had been tried out in Germany on disabled people.

At the Auschwitz-Birkenau camp near Krakow in southern Poland the Nazis were already experimenting with Zyklon B, a cyanide-based pesticide. They used the chemical for the mass gassing of 600 Soviet prisoners and 250 Poles in September 1941.

"Operation Reinhard" led to the construction of three purpose-built extermination camps with gas chambers in occupied Poland.

Once the Belzec, Sobibor and Treblinka death camps were operational in 1942, the Nazis transferred to them inmates of the ghettos. About two million Polish Jews were killed as part of the operation.

'FINAL SOLUTION' INTENSIFIES

The intensification and coordination of the "Final Solution" was agreed at a landmark conference of government ministries and top-ranking Nazi and SS officials in the Berlin suburb of Wannsee on January 20, 1942.

The 15 participants at the Wannsee Conference, convened by Heydrich, agreed that 11 million Jews should be moved to death camps in an operation under the exclusive authority of the SS.

Jews from all over Europe were systematically deported from mid-1942 to six death camps: Auschwitz-Birkenau, Belzec, Chelmno, Majdanek, Sobibor and Treblinka.

At Auschwitz -- which became the symbol of the Holocaust -- more than 1.1 million people were killed, mainly Jews but also Roma.

It was also a work camp where German industry, notably the IB Farben chemical producer, used specially selected workers as slaves.

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© Agence France-Presse