Maria Alekhina and Olga Borisova held for stunt in Yakutsk challenging imprisonment of 'terrorist group' founder Oleg Sentsov.
The pair were taken to a police station in Yakutsk on suspicion of organising an illegal public protest close to the penal colony where Sentsov is held.
They held a large sign saying in English: 'Free Sentsov'.
Alekhina said on her Facebook page: 'Yakutsk, Russia's Republic of Sakha, a bridge across the Lake of Saysary.
The penal colony No. 1, where Oleg Sentsov is held, is twenty minutes, seven and a half kilometres from here.
'We used a linen canvas and pink spray paint to make a banner and placed it on the bridge so that the passers-by and residents of houses across the street could see it.'