In a statement on May 30, the Moscow-based watchdog called on the authorities to immediately release Roman Udot from house arrest, saying that the case against him was politically motivated.

Udot was arrested last week on his arrival from an extended trip abroad and charged with threatening to kill reporters from the state-affiliated television station NTV.

The case stems from a March 2018 incident at a Moscow airport where two NTV reporters descended on Udot and peppered the activist with questions on camera which led to a verbal exchange of insults.

The probe was suspended while Udot was abroad, but when he returned to Russia on May 20 he was detained.

"The situation when employees of propagandist media outlets openly take part in the persecution and humiliation of civil activists is absolutely unacceptable," Memorial said.

The human rights group added that Udot and his wife had been "targeted by so-called journalists of NTV for several years and these actions were either initiated or at least sanctioned by security services."

According to Memorial, Udot's arrest is an attempt by the authorities to hinder Golos's activities during Russia's regional and local elections in September.

On May 24, Human Rights Watch (HRW) said that Udot’s arrest shows the Russian authorities' unwillingness to rein in "abusive tactics" by NTV, which is owned by the Russian state gas company Gazprom.

The New York-based watchdog said in a statement that NTV was "notorious for harassing human rights activists and political opposition members and broadcasting smear campaigns against them."