US National Security Adviser Jake Sullivan said on Sunday that Washington had told Moscow "there will be consequences" if Navalny dies in prison, but did not mention specifics.
Russian Federation has increasingly found itself cornered on many global issues. But the opposition leader's physician, Dr. Yaroslav Ashikhmin, said Saturday that test results provided by the family show Navalny has sharply elevated levels of potassium, which can bring on cardiac arrest, as well as heightened creatinine levels that indicate impaired kidney function.
Russia's penitentiary service on Monday said it was transferring ailing Kremlin critic Alexei Navalny to prison hospital, as the European Union warned it would hold Moscow "responsible" for the state of his health. Moscow insists he is being given adequate care.
Navalny's case has further isolated Moscow at a time when US President Joe Biden's administration has announced tougher economic sanctions and the Czech Republic, a member of North Atlantic Treaty Organisation and the European Union, has expelled Russian spies, accusing Moscow of a role in deadly 2014 explosions at an arms storage depot.
He spoke a day after Biden called Navalny's treatment "unfair" and "totally inappropriate" when asked about it during a round of golf.
Navalny, Putin's most prominent opponent, was arrested in January on returning to Russian Federation from Berlin after recovering from a near-fatal poisoning attack he says was orchestrated by the Kremlin.
He was then jailed for two and a half years the following month over an old embezzlement case, and transferred to a penal colony on February 26.
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The area where officers responded includes a strip mall and several retail stores with a large apartment complex behind it. On Sunday, police swarmed the area searching for 41-year-old Stephen Broderick , who is considered armed and unsafe .
The opposition figure launched his hunger strike last month demanding proper medical treatment over severe back pain and numbness in his limbs.
He wrote: 'I really need a doctor.
Navalny has previously posted online about his declining health since he started the strike, saying that prison wardens had threatened to force-feed him.
Already, Russian authorities have taken their crackdown on Navalny's allies and supporters to a new level, with the Moscow prosecutor's office last week petitioning a court to label as extremist groups Navalny's Foundation for Fighting Corruption and his network of regional offices.
Officers arrested more than 10,000 people during demonstrations that took place in January, in what was the largest show of defiance against Putin in years. Tensions between Moscow and the West are at a new high after Russian Federation moved more than 150,000 troops to the Ukrainian border and following a diplomatic spat between Russian Federation and the Czech Republic.
Russian Federation insists that troops are being stationed along the border in response to North Atlantic Treaty Organisation activities, but the alliance denies any build-up of its own and has called on Putin to "de-escalate" the situation.