By Sarah Rainsford BBC Moscow

At a busy city market, a police officer radios for back-up. "Operation Foreigner" is at its height and the Moscow authorities are cracking down on unwelcome guests.

The offender this time is a young girl: her crime, a missing stamp in her passport. She doesn't look much like trouble, but the officer points out her large bag. "She's from Uzbekistan," he explains, "so she could be carrying drugs".

Human rights worker Alexander Osipov believes that this stop-and-check policy, which deliberately targets non-Slavs, helps fuel a general hostility toward ethnic minorities in Russia.

Extremist groups have grown more visible in Russia

"There is a widely held opinion among police officers, politicians and common people that so-called migrants are people who are inclined to crime," he says.

"They are checked all the time - and not just in the streets. The police come to their flats. This practice violates any legal norms - it is a kind of institutional racism".

The police deny the allegations. Interior Ministry spokesman Sergei Smirnov is adamant the document checks are a crucial part of effective policing.

Violent attacks

"It's not just decent people who come to Moscow," he says, "criminals come too." Operation Foreigner, he says, is a way of exposing them.

"Of course, most of the people we check are dark-skinned, but it's simply a way of preventing crime. There's nothing racist in it."

Singled out for the colour of their skin, Moscow's ethnic minorities have learned to live with random detentions and fines.

Now, though, they are encountering a far more brutal form of racism.

In one of the city's least desirable suburbs, a group of Tajik men sit chatting in their flat as baby Daniel wanders among them, angling for attention. Slightly apart from the others sits Nazarsho.

Racist attacks occur regularly in Moscow

He is in his 30s but looks a decade older, his face grey and drawn. Three weeks ago Nazarsho was beaten unconscious and left for dead on the street by a gang of skinheads.

Like thousands of others from the former Soviet republics, these men came to Moscow as casual labourers, driven by poverty at home. The money Nazarsho earns here helps feed his family back in Tajikistan. But after the attack, he says it is just not worth it anymore.

"We were just on the way home from work when it happened. We could do nothing about it," Nazarsho tells me. He is speaking with difficulty, his head still aching from his injuries.

"I just want to go back to Tajikistan now, there's nothing left for me here. I'm better off at home - poor but safe."

Mood of fear

There are no official statistics on racially motivated crimes but human rights groups believe they are on the rise. The United Nations refugee agency, UNHCR, says it hears of at least ten attacks each month on asylum seekers, and many others go unreported.

Students, too, are bearing the brunt of xenophobia. The Peoples' Friendship University on the edge of town is home to a large percentage of students from Africa and Asia, and has been targeted before.

The police have promised to increase security over the weekend, but the students say that offers little long-term comfort.

President Putin: Condemned extremism

"Today nobody believes that the Russian militia or the government can guarantee their security," says Gabriel Kotchofa, of the Foreign Students Association.

"We are asking only one question - 'how many skinheads have been arrested? How many skinheads have been judged? And where are they now - in what prison?'."

The high profile of the latest racist threats has jolted the authorities into action.

In a measure of how seriously it's being taken, President Vladimir Putin used his state of the nation address this week to condemn extremism.

For the foreign communities here, it is a welcome step against the starkest form of racism.

But if there is to be any hope of the extremists taking the measure seriously, there needs to be a simultaneous fight against prejudice at the very heart of the system.