A lawyer for Vladimir Kara-Murza, an outspoken critic of Russian President Vladimir Putin, announced on Sunday that his client had been allowed to leave Russia for medical treatment as his health slightly improved. Earlier this month, Kara-Murza was admitted to an intensive care unit after experiencing organ failure from being poisoned.

Kara-Murza then reportedly fell into a coma, but Sunday's post on attorney Vadim Prokhorov's Facebook page showed the opposition politician smiling from his hospital bed.

"This morning Vladimir Kara-Murza flew out of the country... to go through rehabilitation treatment after his second acute poisoning," wrote Prokhorov. He did not disclose the location but said as soon as he felt well enough Kara-Murza "will continue to pursue the same course as in past years: activities aimed at the restoration of democracy in Russia."

Putin opponents jailed, poisoned, shot

The 35-year-old Kara-Murza is known for his work with Open Russia, a human rights advocacy group run by Mikhail Khodorkovsky. A former oligarch, Khodorkovsky spent 10 years in prison for tax evasion and money laundering after he openly opposed Putin and accused his government of corruption.

Kara-Murza also worked closely with fellow opposition lawmaker Boris Nemtsov, who was famously shot dead near the Kremlin in February 2015. He was also involved in lobbying work in the United States promoting the expansion of the 2012 Magnitsky Act, which sanctioned Russian elites involved in the death of anti-corruption lawyer Sergei Magnitsky.

In May 2015, Kara-Murza suddenly fell ill during a meeting in Moscow. He was rushed to the hospital, where doctors diagnosed the "toxic influence of an unknown substance." He suffered from kidney failure as a result, but the Russian Investigative Committee refused to launch an inquiry into whether he was the target of an assassination attempt.

He returned to work with Open Russia until his symptoms reemerged a few weeks ago.

The incident is reminiscent of the death of Alexander Litvinenko, a former KGB officer who died from polonium poisoning after meeting with two Russian agents at a London hotel. In exile in England, Litvinenko had written two books that accused the Russian secret services of coordinating false flag operations in order to keep Putin in power.