Russian dissident activist Pyotr Verzilov, who was discharged from a German hospital this week after making significant progress in his recovery, says he is "convinced" he was poisoned by Russia's intelligence services.

"The poisoning was carried out so professionally that no other conclusion is possible," Verzilov said in an interview with the German daily Bild on September 26.

The activist told the BBC he believed he was most likely poisoned by agents of Russia's FSB domestic security agency or GRU military intelligence.

Verzilov, 30, fell ill in Moscow on September 11 with symptoms that his friends say included diminished eyesight and an inability to speak or move.

After his initial treatment in the Russian capital, he was transferred to the Charite hospital in Berlin, which discharged him on September 26 after his health "considerably improved."

Although no traces of a poisonous substance were found in Verzilov's system, the hospital said in a statement that the "absorption" of a poison was the "most plausible explanation" for his ill-health.

"It is possible they tried out a new poison cocktail on me because my poisoning took a different course than others. It didn't take several days before I noticed something but rather was acute right away," Verzilov told Bild.

He said he may have been targeted for his part in a pitch invasion during the 2018 World Cup final between France and Croatia.

Verzilov, who is also a Canadian citizen, was sentenced along with members of the Pussy Riot protest group to 15 days in jail for briefly interrupting the match.

But the activist said he thinks an investigation he was working on into the killing of three Russian journalists in the Central African Republic (C.A.R.) in July was "a more likely reason than the World Cup initiative."

Russian journalists Orkhan Dzhemal, Aleksandr Rastorguyev, and Kirill Radchenko, were killed on July 30 in the C.A.R., where they were working on a documentary about the possible activities there of a shadowy Russian paramilitary group with alleged Kremlin ties.

"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," Verzilov told the BBC.

On the eve of his suspected poisoning, Verzilov told Bild he received news about the deaths, adding, "We cannot comment on this publicly yet, but there is some news."

Verzilov said he had every intention of returning to Russia once he has recovered.

On September 26, Nadezhda Tolokonnikova, a Pussy Riot member and Verzilov's ex-wife, said that he and those close to him were under around-the-clock protection by German police while he received treatment.

In an interview with Current Time TV, the Russian-language network run by RFE/RL in cooperation with VOA, Tolokonnikova said police in Berlin implemented the security measures after a friend of the activist reported being followed by unidentified men.

With reporting by AFP and the BBC