Six activists have been detained near the Kremlin in Moscow for holding invisible signs and calling for the release of other protesters detained earlier.
The group were detained on Sunday in Manezhnaya Square and were holding out their hands as if they were carrying invisible signs.
"Our invisible posters read: Free the 6 May prisoners!" one protester says in the video.
"Because a man was detained earlier holding a poster you could see, we are now holding invisible posters." But the woman is taken away by police and she can be heard saying "You are breaking the law!" as she is dragged away.
The group were protesting against the earlier jailing of anti-Putin demonstrators - part of what is now called the Bolotnaya Square case - in which a group of activists were jailed for protesting against the inauguration of Vladimir Putin for a third presidential term.