Lev Ponomarev, a veteran Russian rights defender who was earlier detained for protesting the Kremlin's military operation in Ukraine, said Friday he has "temporarily" left the country.
The 80-year-old former parliament member has been engaged in activism since the last years of the Soviet Union, helping create the now-dissolved Memorial organization in 1988.
But he said in a statement on Friday that worries about his personal safety, including "shadowy information about what they intended to do to me," have forced him to take a break abroad.
"I doubt that my leave of absence will last long," said Ponomarev, whose name has been added to Moscow's list of "foreign agents" in Russia.
"It will allow me to take care of my health a little and, in a calmer setting, think over the difficult situation in which we all find ourselves."
Ponomarev did not disclose his new location, saying only that he continued to closely follow the "worrying" news in Russia.
Ponomarev confirmed his departure on the same day fellow Kremlin critic Vladimir Kara-Murza appeared before investigators on charges of spreading false information about Russia's military campaign in Ukraine, according to his lawyer.
The charge, which falls under a new law introduced after Russia's Feb. 24 launch of the campaign, could see Kara-Murza, 40, jailed for up to 15 years.
Kara-Murza was due to appear in a Moscow court later Friday, Interfax said.
Russia began sharply intensifying pressure on Kremlin opponents in the months preceding the launch of its military campaign.
After President Vladimir Putin sent troops to the pro-Western country on Feb. 24, independent media outlets have been shut down or suspended operations and many journalists and activists moved abroad.