BUCHAREST, Romania - A Russian trio performing Gypsy music with Madonna on her worldwide "Sticky and Sweet" tour says it regrets the pop star was booed during her Bucharest concert for criticizing widespread discrimination against Gypsies.

Thousands of people applauded the trio's performance with Madonna in Bucharest on Wednesday night. But minutes later they booed Madonna when she said discrimination should end against East Europe's Gypsies, also known as Roma.

In Bucharest on Friday, the Kolpakov Trio said it believes it is the only time the tour has been booed, but declined to say if Madonna had commented about Gypsies at other concerts.

Band member Vadim Kolpakov said "Madonna was surprised" by the booing.

Two members of the band are Roma, while the third is a Russian Jew.