The party led by radical writer Eduard Limonov has been banned in Russia and branded an extremist organization by the authorities.
"All of the detainees, except one girl from St. Petersburg who is under 18, have been released," Alexander Averin said.
"No criminal charges have been pressed so far," he said.
The activists were detained on Saturday morning after entering Red Square under the guise of a wedding procession and holding a rally.
A police spokesman said yesterday the activists had resisted arrest, and that one of them let off a pepper spray in the face of a police officer. He said they could face criminal charges.
On Tuesday Limonov, who has a strong youth following, said he would appeal to the European Court of Human Rights in Strasbourg over the Russian Supreme Court's refusal to lift the ban on his party.
The NBP has pursued 'direct action' tactics by publicly attacking people they considered symbols of President Putin's regime or its allies.
Group members are known to have thrown mayonnaise and tomatoes at prominent public figures, including ex-Prime Minister Mikhail Kasyanov, former NATO Secretary Lord George Robertson, Russian film director Nikita Mikhalkov. Activists have also staged protests by breaking into government offices in Moscow.
For such actions, which the radical group dubs "velvet terror," many of its activists were arrested and sentenced to prison terms.
Since founding the group in 1994, Limonov, 65, dropped his anti-capitalism rhetoric while preserving his nationalist message. In recent years, he has sided with the liberal opposition in Russia, which has been desperate to strengthen its ranks.
