Bernie Sanders says Putin is murdering Navalny 'in front of the world' for exposing the Russian president's 'vast corruption'

• Sen. Bernie Sanders said Putin was murdering Alexei Navalny in "front of the world."
• Navalny's team has said his health is rapidly deteriorating to the point where he could die.
• The Putin critic was transferred to another penal-colony infirmary on Monday.

Sen. Bernie Sanders of Vermont did not mince words as he backed growing calls for the Kremlin critic Alexei Navalny to receive proper medical treatment.

"Make no mistake about what is happening here: activist Aleksei Navalny is being murdered in front of the world by Vladimir Putin for the crime of exposing Putin's vast corruption. Navalny's doctors must be allowed to see him immediately," Sanders said in a tweet on Sunday.

The Russian embassy in Washington, DC, did not immediately respond to a request for comment from Insider.

The Vermont senator's criticism of the Russian president came after Navalny's doctor said he could "die at any moment." The Biden administration has told Russia there will be consequences if Navalny dies.

Navalny has been on a hunger strike for weeks, demanding he receive proper medical care over complaints of back pain and numbness in one of his legs.

The anti-corruption campaigner on Monday was transferred to a prison hospital at a separate penal colony from where he was being held. Russia's Federal Penitentiary Service said Navalny's condition was "satisfactory," according to ABC News.

Meanwhile, Navalny's allies have said his health is rapidly deteriorating and have pushed against referring to the facility he was transferred to as a "hospital."

"Please stop writing that Navalny has been transferred to a hospital. It's not a hospital, it's just a different penal colony that has the same torturous conditions, same everything, apart from the fact that there are few formally qualified doctors on-site. This changes nothing," Maria Pevchikh, an investigator at Navalny's Anti-Corruption Foundation, said in a tweet.

In August, Navalny was poisoned with the nerve agent Novichok, which can cause lingering health effects. Navalny blamed Putin for the incident. Leaders across the world condemned Putin over the poisoning. The Russian president's critics have often been killed in violent or mysterious ways.

In September, Navalny was taken to Germany for medical treatment. Upon returning to Moscow in January, he was arrested and accused of violating parole - including while he was in Germany - over a 2014 suspended sentence for fraud. Navalny, who's maintained all charges against him are politically motivated, was sentenced to 2 1/2 years in prison.