Thousands of Russian nationalists planned to march in Moscow on Monday in an annual show of anger against the presence of Muslim migrants that has previously spilled into violence.

The city-sanctioned demonstration was to take place through the same blue-collar region on the city’s outskirts that saw riots break out three weeks ago over a stabbing murder blamed on a citizen of Azerbaijan.

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Organizers hope to bring up to 30,000 people out on the streets in a show of Slavic pride.

The so-called “Russian March” — an annual event coinciding with a new Unity Day holiday President Vladimir Putin introduced to commemorate the expulsion of Poles from Moscow in 1612 — has been previously accompanied by violent attacks against ethnic minorities and foreigners working in the city.

The U.S. embassy in Moscow urged Americans to steer well clear of the protest and be diligent throughout the day.

“Extreme violence has been witnessed during previous nationalist protests, and spontaneous demonstrations of support may appear anywhere throughout the city, at any time of the day,” the US embassy said in special security message.

Analysts and Kremlin critics have long accused Putin of fostering dangerous nationalist sentiments in society in order build a broad-based coalition of middle-class Russians around his rule.

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Ethnic tensions have grown in Moscow and other major cities that have been flooded by migrant laborers from poor Muslim regions of the Caucasus and Central Asia.

The workers often endure hazardous labour and living conditions and are increasingly regarded with disdain by many Muscovites.

The tensions came to a boil on October 13 when a crowd of thousands chanting “Russia for Russians!” and other neo-Nazi slogans rioted in the southern Biryulyovo district following the murder of a young Muscovite.

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Smaller protests continued until city authorities arrested a man from Azerbaijan who worked at the vegetable warehouse where the stabbing occurred.

Ways to stem the migration of ethnic Muslim laborers was also a major theme of Moscow mayoral elections in September that Putin ally Sergei Sobyanin won over opposition leader Alexei Navalny — a nationalist who has attended previous “Russian March” rallies.

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Navalny said he still believed in the need to rid Moscow of migrants but would not be joining Monday’s demonstration.

“I still support the Russian March as an idea and as an event,” Navalny wrote in his blog.

“But today, my participation in the Russian March would turn into a hellish comedy,” Navalny said in reference to the growing media attention he has been gaining both in Russia and abroad.

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Putin meanwhile planned to commemorate Unity Day by attending an exhibit honoring the Romanov dynasty together with Russian Orthodox Church Patriarch Kirill.