Russian police say they are searching for other members of Pussy Riot, the punk band whose anti-Putin protest inside a Moscow cathedral led to prison sentences for three of the activists.
Five women wearing bright-colored balaclavas took part in the provocative protest in February, but only three were identified and arrested.
Police said Monday that they were trying to determine the identities and locations of several other women.
The announcement was seen as a warning to Pussy Riot to stop its protests against President Vladimir Putin. The band released its latest anti-Putin song on Friday, the day three of its members were sentenced to two years in prison as part of a broader crackdown on the opposition.
The verdict was criticized by the U.S and European governments.