MOSCOW, (Reuters) – Russia has taken two of its Kremlin enemies, Alexei Navalny. On Tuesday, a prominent activist for the opposition said that Russia had detained them. He also suggested that they might face extremeism charges, which can lead to long sentences.

Russian authorities in recent months have cracked down against groups associated with Navalny (45), who is President Vladimir Putin’s most vocal critic. For parole violations in a case of fraud he claims was politically motivated, he is currently serving two and a half years.

A Russian court found that Navalny was an ‘extremist’ anti-corruption foundation in June.

Then authorities launched an investigation into campaign workers on extremism charges after the allies of his regrouped around a network of organizations set up in Russia for September’s parliamentary elections.

State investigators took the ex-heads of Siberian provincial elections headquarters to Tomsk, Irkutsk, on Tuesday. They also interrogated Leonid Volkov (a Navalny ally who lives in exile) via Telegram.

Volkov claimed that he tried to convince both Kseniya Fareeva and Zakhar Sarpulov to leave Russia as he has done with a few other dissidents, but was unsuccessful.

For comment, the Investigative Committee could not be reached immediately by the State Body charged with investigating and pressing charges.

Navalny flew to Germany in the last year after suffering from poisonings in Siberia and Germany with what Western experts deemed was Novichok military nerve agent.

Russia denied involvement in the poisoning, and the experts rejected their findings. The West responded by imposing new sanctions on Russia.