Berlin, Sep 18 (IANS): A German doctor on Tuesday said there was a "high plausibility" that a member of the Russian protest group Pussy Riot who was flown to Berlin for specialist medical treatment after falling ill in Moscow last week, was poisoned.

Pyotr 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.

Speaking to the media, doctor Kai-Uwe Eckardt of the Berlin Charite Hospital said that an external substance appears to have affected Verzilov's nervous system and medics have been unable to determine the source, CNN reported.

The activist remains in intensive care but is recovering, Eckardt said.

Verzilov flew into Berlin on Saturday, according to Germany's Cinema for Peace Foundation, a non-profit humanitarian group that has previously advocated for Pussy Riot and which organized the flight.

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

Verzilov was one of four members of the group to invade the pitch, dressed in a police officer's uniform, during the World Cup final between France and Croatia on July 15.

It was part of a protest against Russian police brutality after a series of torture allegations were reported from prisons and police interrogation rooms across the country.