RUSSIAN police have restored order to the streets of Moscow, after days of race riots that left scores of people wounded and led to more than 3,000 arrests.
The immediate reason for the violence was the murder of a local Russian, allegedly by an ethnic Chechen of Muslim faith who is yet to be identified.
But tensions between Russians and the predominantly Muslim ethnic minorities have been simmering for years and represent a significant, enduring challenge to President Vladimir Putin.
Islam has long been Russia's second-biggest religion, after the Orthodox strand of Christianity, which is the country's predominant faith.
However, for much of the past century this had scant impact on the lifestyle of the average Russian, since the overwhelming majority of Muslims lived in remote communities.
This changed following the collapse of the Soviet Union. Chechen Muslims - who have always held Russian citizenship - moved from their historic hamlets in the Caucasus to Moscow. And they were followed by various ethnic groups from the newly independent republics of Central Asia.
No reliable figures for these migration flows are available. But observers estimate that 800,000 Kyrgyz and three million Uzbeks live in Russia, out of populations of 5.4 million and 28.2 million, respectively, in the two Central Asian states of Kyrgyzstan and Uzbekistan.
And in Tajikistan, the poorest country in Central Asia, as many as 1.5 million of its 6.9 million people work abroad, the vast majority of them in Russia. According to data from Russia's labour ministry, up to 40 per cent of construction workers nationwide are migrants, mostly Muslims.
Nowhere is this changing ethnic landscape more evident than in Moscow, a city of 11 million inhabitants, among them 2.5 million Muslims.