Russia took tough measures against illegal immigration in a drive to boost jobs for Russians, disrupting retail markets across the country that rely on migrant workers.

The measures are aimed at enforcing a new quota on the number of immigrants coming from other former Soviet republics whose citizens are exempt from Russian visa requirements.

The quota has been set at six million people for 2007, meaning that up to half the 12 million foreigners said by the federal migration service to be working illegally in Russia could be deported.

The new laws impose set fines for employers of up to 30,000 dollars (23,200 euros) for each illegal immigrant found at work.

"We are cleaning up the markets for domestic producers," said Denis Soldatikov, a spokesman for the federal migration service.

The laws "will regulate the situation with around 12 million foreigners working illegally in Russia and so will offer more jobs to Russian citizens," said Soldatikov.

Television images showed markets in Vladivostok in far eastern Russia and Rostov-on-Don in the southwest lying nearly empty. One Moscow market, Cheryomushkinsky, was shut down last week for immigration breaches.

Last year President Vladimir Putin called for more Russians to be given jobs in food markets, where many stallholders come from former Soviet republics in the Caucasus and Central Asia.

A government order has also come into force this month limiting the proportion of foreigners working at retail markets to 40 percent by April and to zero by the end of the year.

The measures have come under criticism from human rights and advocacy groups, including the International Organisation for Migration, which argue that the changes have not been thought through.

Another law that went into effect on Monday theoretically should ease the compulsory registration procedure for immigrants. But experts said that new arrivals will continue to face difficulties in gaining legal status.

Russia has one of the highest illegal immigration rates in the world and Russians often complain about the high number of foreigners.

Anti-immigrant movements, as well as violent racist groups, have gained large followings in recent years.

"Illegal immigration is a huge problem in Russia," Sergei Fateyev, leader of the Mestnye nationalist youth group, told reporters at a small demonstration against illegal immigration in Moscow on Monday.

The demonstration, attended by some 40 people, was held outside the embassy of Azerbaijan, a former Soviet republic that is a major source of migrant labourers.

Illegal immigrants often work as builders, vendors and cleaners -- relatively poorly paid menial jobs that some experts say many Russians would not be willing to accept.

The lack of proper housing makes registering at a fixed address, as required by the law, nearly impossible for many immigrants forced to live in temporary housing or shelters and often discriminated against by landlords.

"We are looking for vendors with Russian citizenship," read a sign stuck on the main entrance door to a market in the southwest Moscow suburb of Konkovo.