* Detentions follow worst anti-migrant violence in 3 years
* 380 arrested Sunday night after migrant market stormed
* Advocacy groups warns migrants of heightened attack risk
Russian police rounded up more than 1,000 migrants on Monday in a Moscow neighbourhood where rioting erupted a day earlier over a fatal stabbing of a Russian that many residents blame on a man from the Caucasus region.
An advocacy group warned migrants from the mainly Muslim Caucasus and Central Asia of an increased risk of attacks after the worst ethnic disturbance in the Russian capital in three years.
About 1,200 people were detained at a wholesale vegetable market that had been stormed on Sunday night by rioters after a protest over the stabbing death of an ethnic Russian man, police spokesman Alexei Shapkin said.
The detainees were taken to police stations and police will seek to determine whether they were involved in any crimes, he said. Televised footage showed detainees standing against walls or lined up in front of camouflage-clad police.
By rounding up migrants, authorities seemed to be trying to appease residents who had rallied in the Biryulyovo district to demand police find the killer of Yegor Shcherbakov, 25, and take more action to prevent crimes by migrants.
Shapkin said police found a car at the warehouse with three pneumatic pistols, two knives and a baseball bat inside.
On Sunday, a mob in the southern neighbourhood smashed shop and vending stalls, fought with police and stormed the vegetable market in the biggest outbreak of anti-migrant violence in Moscow in three years.
Police arrested at least 380 people as they struggled to quell the violence, which injured several police and others and shone a spotlight on persistent tension between ethnic Russians and people from the Caucasus and Central Asia.
Migrant labour has played a significant role in Russia's transformation during a oil-fuelled economic boom that took off around the same time President Vladimir Putin came to power in 2000.
But many in Moscow chafe at the influx of migrants from Russia's heavily Muslim North Caucasus and ex-Soviet states of the Caucasus and Central Asia, though many do low-paying jobs, such as in construction, that few local residents want.
A group that advocates for labour migrants in Russia warned of an increased risk of ethnic violence in Moscow on Monday.
Mukhamad Amin, head of the Federation of Migrants of Russia, said extremists had seized upon the killing to cause havoc.
"The nationalists are pursuing their political goals. This is clearly very dangerous. We are warning migrants to be careful for now in crowded areas and on public transportation."
The rioting came before Eid al-Adha, an Islamic holiday that most Russian Muslims begin celebrating on Tuesday. In Moscow, ethnic tension is often higher during such holidays because large numbers of Muslims gather at the city's few mosques.
Putin has frequently warned of the dangers of ethnic and religious violence in multicultural Russia, which is mostly Slavic and Orthodox Christian but has a large Muslim minority concentrated in the North Caucasus and a few other regions.
Putin said this month that Russia needed migrant labourers in industries such as construction but, in a nod to anti-migrant sentiment, he suggested their numbers could be restricted in some other sectors including trade.
He also suggested the Kremlin would resist calls by some Russians to establish visa regimes with several former Soviet republics, indicating this would undermine reintegration efforts that he has made a priority in a third presidential term.