Allies of jailed Kremlin critic Alexei Navalny are planning the largest street protest in modern Russian history this week to highlight his failing health from a hunger strike that has lasted nearly three weeks.
"Things are developing too quickly and too badly," they wrote on Navalny's website, announcing their plans for nationwide protests. "We can no longer wait and postpone. An extreme situation demands extreme decisions."
Russia regards the protests as illegal and used force to break up demonstrations in the past. The latest protests are planned for Wednesday to coincide with President Vladimir Putin's annual state of the nation speech to the political elite.
Navalny, a fierce opponent of the Kremlin, started to refuse food on March 31 in protest against what he said was the refusal of prison authorities to provide him with adequate medical care for acute back and leg pain.
On Saturday, a medical trade union with ties to Navalny said he was in a critical condition, citing medical tests that it said showed that his kidneys could soon fail, which could lead to cardiac arrest.
In February, he was sentenced to jail after returning to Russia from Germany, where he had treatment for a nerve-agent poisoning attack that he blamed on Mr Putin.
The US on Sunday warned Russia that there would be consequences if Navalny died in jail.
Prison authorities say they offered him proper medical care but that Navalny, 44, refused it and insisted on being treated by a doctor of his choice from outside the jail, a request they declined.
Russia's ambassador to Britain told the BBC that Navalny was attention-seeking, but that Moscow would ensure he lived.
"He will not be allowed to die in prison but I can say that Mr Navalny … he behaves like a hooligan, absolutely," Andrei Kelin said.
"His purpose for all of that is to attract attention."
Navalny previously said prison authorities threatened to put him in a straitjacket and force-feed him unless he accepted food.
His supporters face the prospect of their movement being officially outlawed and declared extremist, a move that would expose activists to the possibility of lengthy jail terms.
Navalny's allies declared a moratorium on protests after staging three demonstrations at the height of winter. Thousands of people were detained by authorities.
Some protesters were unhappy that the demonstrations were halted, but organisers said they would hold a major protest once 500,000 people registered online to take part.
In light of Navalny's poor health, organisers said they were calling the protest on Wednesday, despite being about 40,000 people short of their target.
"Navalny is now in a prison camp and his life is hanging by a thread. We don't know how much longer he can hold out," they said.
The Kremlin has cast Navalny as US-backed subversive on a mission to destabilise Russia.
