Video footage showing the protesters demonstrating on Manezh Square with "invisible posters." (YouTube / Pavel Elizarov)
Six activists have been detained in Moscow for holding "invisible posters" and calling for the release of protesters who were jailed for participating in an opposition rally in May 2012.
In a video posted on YouTube on Sunday, several protesters are shown standing outside the State Historical Museum on Manezh Square with their arms held aloft as if holding real signs. A female demonstrator told opposition-minded news website grani.ru that their "invisible posters read: Free the 6 May prisoners!"
"Because a man was earlier detained for holding a poster you could see, we are now holding invisible posters," the woman said, adding that police were not yet used to that type of protest.
Police are then shown leading the protesters away, while the female protester repeatedly shouts that they are being detained illegally.
In February, seven people were sentenced to between 2 1/2 and four years in prison for participating in an anti-Kremlin rally on Moscow's Bolotnaya Ploshchad on May 6, 2012, which ended in clashes between demonstrators and police.
Critics have said that the case was politically motivated, and formed part of a wider crackdown on Kremlin opponents.