Several prominent Kremlin critics were released from police custody on Saturday following an unprecedented raid on a political conference.

Moscow police previously said some 200 people had been detained while attending a summit on municipal politics.

The conference saw opposition leaders and independent local officials from different parts of Russia travel to Moscow to coordinate its strategy against the ruling United Russia party.

Shortly after the kickoff, however, police broke up the gathering and arrested nearly all participants, as well as some journalists covering the event.

Authorities said that a "significant part of the attendants lacked the means of [anti-virus] protection."

Links to 'Open Russia'?

Moscow police also said some of the participants were "members of [an] organization whose activities were declared undesirable" on Russian territory.

The "undesirable" designation stems from a controversial law that targets foreign organizations in Russia. Groups that fall under that category are barred from issuing publications in Russia. People cooperating with such organizations risk fines and jail time.

While the police did not specify the organization in question, it seemed very likely they were referring to "Open Russia," backed by exiled energy tycoon Mikhail Khodorkovsky. Several of the group members were present at the gathering.

What do opposition leaders say?

Opposition activist Vladimir Kara-Murza spoke to reporters following his release, saying that the participants would be expected to appear before court at a later date.

"I think Franz Kafka would simply be envious of the Russian judiciary today, he wouldn't have the imagination," he said.

Kremlin critic Ilya Yashin, an aide to jailed opposition leader Alexei Navalny and leader to one of Moscow's municipal districts, posted a video of his arrest.

"The government obviously believes it is demonstrating force. In reality, all these cops running around — it seems just pitiful and ugly," he wrote on Twitter.

In a separate Facebook post, Yashin also noted that "no one promised us freedom on a silver platter."

He later confirmed his own release.

Pro-Putin party polls low

Russia is set for a parliamentary election this fall.

The United Russia party currently hold 335 out of 450 seats in the assembly, but recent polls show a drop in the ratings — only 27% of voters are planning to endorse the pro-Putin party at the ballot, according to the reputable Levada-Center.

dj/rs (dpa, AFP, Interfax)