Members of the punk band Pussy Riot have been beaten with horsewhips during an attempt to perform in the host city of the Russian Winter Olympics.
Video footage shows five members of the Russian group, dressed in their signature bright colours and head masks, attempting to perform a song under a sign advertising the Sochi Games.
At least 10 Cossacks are seen quickly approaching and firing pepper spray at the band members.
When they continue to sing and dance, the Cossacks use horsewhips to strike several of the women and one male supporter. Some were violently unmasked and led away.
Maria Alyokhina and Nadezhda Tolokonnikova, who were jailed for their role in a protest against President Vladimir Putin in Moscow's main cathedral, were among those who took part.
Ms. Alyokhina tweeted an image of blood dripping down the face of a supporter after the attack. Another photograph showed red marks left on the chest of Ms. Tolokonnikova.
Ms. Tolokonnikova tweeted "Under the banner Sochi 2014, to the sound of (the song) 'Putin will teach us to love the homeland', Cossacks attacked Pussy Riot, beat us with whips and sprayed a lot of pepper gas at us".
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The incident comes a day after Ms. Alyokhina and Ms. Tolokonnikova were briefly detained in Sochi on suspicion of robbery. They were later released.
Ms. Tolokonnikova said they were also detained for several hours on Sunday and Monday, but not arrested.
Pussy Riot has called for an international boycott of the Sochi Games, warning that any world leader who attends the event is effectively expressing support for Mr. Putin.
Ms. Alyokhina and Ms. Tolokonnikova were released from prison in December. They were among several political prisoners freed under an amnesty bill, considered by some to have been an attempt by Mr. Putin to silence critics in the run-up to the Games.
The Cossack patrolmen have made no comment on Wednesday's incident.
Cossacks, who are neither members of the police or the military, have been employed by Russia to maintain order and help patrol the streets in the Krasnodar province, where Sochi is located.
Mr. Putin has staked his reputation on the Winter Games, hoping they will show the world Russia's modern face more than two decades since the fall of the Soviet Union.
