MOSCOW, September 16 (RAPSI) – More than 3,000 people were detained during police raids in the Moscow Metro system over the weekend, the Interior Ministry’s press-service told RIA Novosti.

More than 550 administrative and 4 criminal cases were opened as a result. “The weekend raid resulted in 4 criminal cases, which included drug trade and illegal weapons possession,” the police representative told the journalists.

He added that 3,122 people were detained by the police, and 564 administrative cases were initiated, with 52 counts of migration law violations, 69 counts of minor hooliganism and more than 350 for disorderly conduct.

The Moscow subway has one of the world’s busiest rapid transport systems, consisting of almost 200 mostly underground stations, stretches more than 300 kilometers carries almost 2.5 billion passengers a year, according to its 2012 figures. It remains the cheapest and most reliable transport in the Russian capital, which suffers of some of the world’s worst traffic jams.

The “decriminalization” sting follows last month’s crackdown on illegal immigrants in Russia’s capital.

Hundreds of immigrants, most of them from Vietnam, were placed in a tent camp in Moscow over alleged violation of migration rules after massive raids on Moscow markets and other migrant workplaces in August. The raids followed an attack on a police officer who was seriously injured at a market while trying to detain a suspected sex offender.

Economic growth driven by revenues from oil exports and a dwindling domestic labor force have attract millions of labor migrants, many of them the former Soviet republics of Central Asia. Some 11.3 million foreigners entered Russia this year, of whom 3 million work illegally, the Federal Migration Service said in late July.