Kremlin critic Navalny's life 'in the balance,' aide says as he calls for protests

Leading Kremlin critic Alexei Navalny's "life hangs in the balance" as he continues his hunger strike in prison, one of his closest aides said in a video Sunday, as he called for mass protests across Russia.

"We don’t know how long he can hold on. But it is clear we do not have time," Leonid Volkov, one of Navalny's top strategists, said in the video posted on YouTube and Navalny's website.

Calling for demonstrations across Russia on Wednesday, Volkov said the short notice was because Navalny's "life hangs in the balance." The 44-year-old's condition was critical, he added.

Navalny, President Vladimir Putin’s most visible and persistent critic, started a hunger strike 18 days ago to protest prison authorities’ refusal to allow him to be seen by a private doctor for diagnosis of severe back pain and loss of feeling in his legs.

The Russian penitentiary service says he is getting adequate care.

But White House National Security Advisor Jake Sullivan told CNN Sunday there will be consequences if Navalny dies in custody.

"We have communicated to the Russian government that what happens to Mr. Navalny in their custody is their responsibility and they will be held accountable by the international community," he said.

On Saturday, Dr. Yaroslav Ashikhmin said test results he received from Navalny’s family showed sharply elevated levels of potassium, which could lead to cardiac arrest, and signs of kidney failure.

“Our patient could die at any moment,” he said.

There was no immediate comment from police or government officials about the call for protests, but the response is likely to be harsh.

Police arrested more than 10,000 people during nationwide protests in January, calling for Navalny to be freed among other demands.

After that, Navalny's team declared a moratorium on the demonstrations to prevent violence, saying they would hold a big protest once 500,000 people had registered online to take part.

While that number has not quite been reached, with nearly 460,000 registered so far, Volkov said the time to act was now. "It is no longer possible to wait and postpone," he said. "An extreme situation requires extreme solutions."

On Friday, state prosecutors in Moscow asked a court to label Navalny’s anti-corruption group, which has investigated the Kremlin elite and Putin himself, and its regional headquarters “extremist” organizations, Russian state news agency Tass reported. Human rights organization Amnesty International called it "new attempt to fully shut down dissent" in Russia.

The Wednesday protests have been called for symbolically resonant locations — Manezh Square in Moscow, just outside the Kremlin walls, and St. Petersburg’s sprawling Palace Square.

Navalny was arrested on Jan. 17 when he returned to Russia from Germany, where he had spent five months recovering from Soviet nerve-agent poisoning that he blames on the Kremlin.

Russian officials have denied any involvement and even questioned whether Navalny was poisoned, which was confirmed by several European laboratories.

Navalny was ordered to serve 2 1/2 years in prison on the grounds that his long recovery in Germany violated a suspended sentence he had been given for a fraud conviction in a case that Navalny says was politically motivated.

Reuters and the Associated Press contributed to this report.