Survivors have paid homage at the Auschwitz-Birkenau camp to an often forgotten genocide, that of the Roma people, on a key 75th anniversary.

In addition to the six million Jews killed in camps such as Auschwitz, the Nazis killed other minorities during the Second World War, including between 250,000 and 500,000 Roma and Sinti.

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Broadly speaking, Sinti are people who arrived from India and settled in Western and Central Europe many centuries ago, while Roma are centred largely in Eastern Europe.

Since the term gypsies is considered offensive, the groups are collectively usually referred to as Roma.

US civil rights leader the Reverend Jesse Jackson drew comparisons between the suffering of the long-persecuted minority in Europe with that of African Americans.

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In turn, a German Roma leader, Romani Rose, said that the African American struggle that made vast achievements in the 20th century was a model and inspiration for his people, who still face marginalisation and violence.

Bowing his head as he began a visit of the camp ahead of official ceremonies, the 77-year-old Mr Jackson, a Baptist pastor, prayed that such horrors never occur again.

He appeared deeply moved as he visited a surviving gas chamber and crematorium and visited an exhibition depicting the mass murder of Roma and Sinti.

During official ceremonies before a large crowd of diplomats and Roma from across Europe, he warned of the dangers presented by a resurgence of racism and white nationalism.

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Other dignitaries at Friday's observances were Germany's deputy foreign minister, Michael Roth, who before his visit lamented the lack of broad knowledge about the systematic murder of the Roma communities during the Second World War.

"For too long we have pushed the genocide of over 500,000 Sinti and Roma out of our historical memory and allowed the largest ethnic minority in Europe to be pushed to the margins of our society," Mr Roth said recently.

"We have the responsibility to ensure that the stories of the victims' suffering not be forgotten and that anti-Gypsy prejudices disappear from people's minds."

The commemorations in southern Poland, which was under German occupation during the Second World War, fall exactly 75 years after thousands of the last remaining prisoners in the so-called Gypsy family camp at Auschwitz-Birkenau were killed.

Organisers said that around 20 survivors, most of them Roma and Sinti but also some of them Jewish, were joining Friday's commemorations, which have been organised by the Central Council of German Sinti and Roma and the Roma Association in Poland in cooperation with the Auschwitz-Birkenau State Museum.

During the war, members of the Roma community faced deportation, sterilisation, mass shootings in Soviet-occupied territories as well as the gas chambers.

Many perished from starvation and disease.

Despite their immense suffering, it took decades for them to achieve even small measures of recognition and justice.

It was only in 1982 that then West German chancellor Helmut Schmidt publicly declared that Sinti and Roma "were persecuted for reasons of race" and that "these crimes constituted an act of genocide".

More progress has come of late.

In 2012, Germany erected a memorial in Berlin.

Three years later, the European Parliament declared August 2 to be European Roma Holocaust Memorial Day.

And this year before International Roma Day on April 8, a bipartisan resolution was introduced in the US Congress that said "Roma enrich the fabric of our nation" and that they have been "part of every wave of European migration to the United States since the colonial period, tying our country to Europe and building the trans-Atlantic bond".

In a statement on Friday, US secretary of state Mike Pompeo called "on all governments to take steps to combat intolerance against the Roma and to enable their full participation in civic and economic life."

Recently, Pope Francis has highlighted the discrimination that Roma still face today, even in Rome.