* Killing of ethnic Russia led to rioting in southern Moscow
* Police say detain migrant outside of Moscow
* Advocacy groups warn migrants of heightened attack risk
Russian police detained hundreds of nationalist youths on Tuesday who gathered to protest over the killing of an ethnic Russian in southern Moscow, hours after authorities arrested a migrant labourer suspected of the slaying.
The killing of Yegor Shcherbakov, 25, unleashed earlier this week the worst race riots Moscow has seen in three years and nationalists threatened further protests in areas populated by migrant workers from ex-Soviet Central Asia and Caucasus states.
Advocacy groups warned migrants of a high risk of violence as crowds of Muslims celebrated the Islamic holiday of Eid al-Adha, and a heavy police presence was seen in the capital.
Police said they had detained a native of the mostly Muslim state of Azerbaijan, Orhan Zeynalov, who is suspected of fatally stabbing Shcherbakov in front of his girlfriend while they were walking home on Thursday night.
The murder triggered the riots in Moscow's southern Biryulyovo district, where Shcherbakov was attacked.
Police said Zeynalov resisted special forces when they tried to detain him in Kolomna, a small town outside Moscow, Russian news agencies reported.
Tensions simmer in Moscow between disenchanted ethnic Russian youths and labour migrants mostly from predominantly Muslim ex-Soviet states.
Hundreds of nationalists gathered near a shopping centre in southern Moscow, Russian wires said, to protest against Shcherbakov's killing in what was promoted online by nationalists as an "Answer to Eid al-Adha".
City police official Oleg Sigunov was quoted by RIA as saying that 276 young people had been detained on their way to the protest.
Earlier in the day, police set up barriers and metal detectors outside Moscow's main mosque. Ethnic tension is often higher during the Islamic holiday because crowds spill out into the streets around the city's few mosques.
Crowds of residents in Biryulyovo have called for tougher policing of migrants and roamed the streets hunting for men who matched a police description of Shcherbakov's alleged killer.
One of Russia's main Muslim organisations said its website was also hacked on Tuesday.
On Sunday, rioters smashed shop windows, clashed with police and stormed a market in Biryulyovo where many migrants work.
The violence was the worst in Moscow since 2010 when some 7,000 nationalists rallied near the Kremlin, chanting racist slogans and attacking non-Slavic-looking passers-by in what then-President Dmitry Medvedev called "pogroms".
On Monday, police also raided the market in Biryulyovo and detained more than 1,200 people to check for any wrongdoing, and about 450 migrants were detained at another site.
In an apparent move to appease residents, Moscow's police chief fired the senior officer in the district on Tuesday.
Migrant labour has played a significant role in Russia during an oil-fuelled economic boom that took off around the time President Vladimir Putin came to power in 2000.
But many in the capital resent the migrants, and some Russians have called on the government to impose visa requirements for people arriving from Moscow's former satellites.