Russian human rights activists picketed immigration service offices in St. Petersburg this week, protesting the holding of migrant workers in detention camps.

The activists -- who were denied permission to hold a mass rally outside the offices of the General Directorate of the Federal Migration Service in St. Petersburg, instead gathered in small groups for pickets Tuesday -- when they distributed leaflets criticizing the detention of hundreds of recently arrested migrants in a series of makeshift camps.

The picketers, organized by the Russian liberal movement Solidarity, denounced the "gulag-like" detention centers, set up after hundreds of migrants were rounded up in police raids in recent weeks across Russia -- including about 1,000 people, mostly Vietnamese, arrested in Moscow since late July.

Carrying placards with slogans such as "Moscow -- the capital of the Gulag," and "Rehearsal? Today, migrant guest workers, tomorrow...?" protesters called the detention centers "a system of concentration camps created in Russia," RIA Novosti reported.

"The real problem of illegal immigration cannot be solved by gross violations of human rights," protester Joseph Skakovskii told the news agency.

Along with Vietnamese, migrants from Egypt, Morocco, Syria, Kyrgyzstan, Azerbaijan and Uzbekistan working in sweatshops were also arrested during the police operation in Moscow, with many of them being held at a camp in the city's eastern district of Golyanovo.

Protester Igor Andreev told Radio France Internationale the camps are reminiscent of the banishment of dissidents to gulags during the Soviet era, adding some believe they are serving as dress rehearsals for the mass jailings of political opponents of Kremlin-backed Moscow mayoral incumbent Sergei Sobyanin in his Sept. 8 election against protest leader Alexei Navalny.

"In Moscow they expect this is what would happen if Sobyanin does not win ... and [the government] is preparing for this, of course.

"And we've been through this before," he added. "There used to be 'enemies of the people,' even entire nations were evicted such as Chechens, Kalmyks, and so on. Then there were the dissidents."

RFI reported police approached each of the picketers, copied passport details and strictly reminded them that pickets must comply with laws requiring them to stay a certain distance away from the FMS headquarters.

Police also recorded picketers' interviews with journalists on camcorders.

"The fact is that today there are no citizens of Russia in these camps, but there is no guarantee that tomorrow they will not include Russian citizens, such as political opposition, sexual minorities, and maybe some religious groups," Lyudmila Oak, co-chairwoman of the St. Petersburg Solidarity branch, told the French broadcaster.

Human Rights Watch said last week the Golyanovo camp was set up after jails were filled to overflowing with migrant workers, who were being held in tents with "no electricity, no communications, appalling sanitation conditions, inadequate food, and lack of access to potable water."

Some who are awaiting deportation are asylum seekers or have lawful residence permits, and thus have a legal right to be in Russia, HRW said.

Russia's human rights ombudsman, Vladimir Lukin, said Monday the Golyanovo camp will be closed in the coming days, RIA Novosti reported.

He indicated in statement that after a visit to the camp last week, "representatives of the Moscow government assured me that the camp ... will be closed in the next few days and its residents will be transferred to a place more adapted to their presence until they are expelled from the Russian Federation."