Moscow, Sep 27 (IANS): A leading activist from Russian protest group Pussy Riot who is believed to have been poisoned has laid the blame on the government's intelligence services.

"The poisoning was carried out so professionally that no other conclusion is possible," Pyotr Verzilov told the BBC on Thursday.

The activist said he believed he was most likely attacked either by Russia's FSB domestic security agency or GRU military intelligence.

"The actions we do are as loud as anything happening in Russia, so for them it's quite a big deal and that's just the price you have to pay if you want Russia to change," he said.

Verzilov, who ran on to the pitch during the FIFA World Cup final, reportedly fell ill after a court hearing in the Russian capital on September 11 and was taken to hospital in a serious condition.

He was flown to Berlin four days later for specialist medical treatment.

The Berlin Charite hospital where he was treated issued a press release on September 18 stating Verzilov was admitted with "symptoms of poisoning".

The activist also told Germany's Bild newspaper they could have tried a "new cocktail of poisons" on him as his symptoms were more immediate "than others".

The Russian punk band, known for obscuring their identities with colourful balaclava-style masks, is an outspoken critic of President Vladimir Putin's government.