Moscow. Police in Russia have arrested more than 1,200 people in a raid targeting migrants after major riots in Moscow.The "preventative raid” targeted workers at a vegetable warehouse, which was attacked by demonstrators on Sunday, Russian news agencies reported.Angry protesters overran the market searching for migrant workers.The rioting began during a protest over the death of an ethnic Russian man on Thursday allegedly by a Muslim migrant from the North Caucasus.Ethnic Russian Yegor Shcherbakov, 25, was killed in front of his girlfriend in the capital’s Biryulyovo district.Police have released a security camera photo of the suspect, but have not identified him. Media said the image suggested the man was of "non-Slavic appearance”, leading nationalists to conclude the killer was a Muslim migrant from the Russian North Caucasus.Some 380 people were detained during the rioting that began on Sunday, but most have been released without charge.It is unclear what charges, if any, those detained in Monday’s raid against migrants in the vegetable warehouse would face, RIA Novosti reported. Police were quoted as saying that they were investigating "involvement in criminal activity”, without elaborating.The issue of immigration and internal migration was one of the main issues in Moscow’s recent mayoral election won by Sergei Sobyanin.The BBC’s Steve Rosenberg in Moscow says the violence reflects Russian nationalism, and the growing tension between ethnic Russians and migrants from the Caucasus region and from former Soviet republics.