Madonna booed in Bucharest ...

At first, fans politely applauded the Roma performers sharing a stage with Madonna. Then the pop star condemned widespread discrimination against Roma, or Gypsies — and the cheers gave way to jeers.

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The sharp mood change that swept the crowd of 60,000, who had packed a park for Wednesday night's concert, underscores how prejudice against Gypsies remains deeply entrenched across Eastern Europe.

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Despite long-standing efforts to stamp out rampant bias, human rights advocates say Roma probably suffer more humiliation and endure more discrimination than any other people group on the continent.

Sometimes, it can be deadly: In neighboring Hungary, six Roma have been killed and several wounded in a recent series of apparently racially motivated attacks targeting small countryside villages predominantly settled by Gypsies.

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"There is generally widespread resentment against Gypsies in Eastern Europe. They have historically been the underdog," Radu Motoc, an official with the Soros Foundation Romania, said Thursday.

Roma, or Gypsies, are a nomadic ethnic group believed to have their roots in the Indian subcontinent. They live mostly in southern and eastern Europe, but hundreds of thousands have migrated west over the past few decades in search of jobs and better living conditions.

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Romania has the largest number of Roma in the region. Some say the population could be as high as 2 million, although official data put it at 500,000.

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Until the 19th century, Romanian Gypsies were slaves, and they've gotten a mixed response ever since: While discrimination is widespread, many East Europeans are enthusiastic about Gypsy music and dance, which they embrace as part of the region's cultural heritage.