The US warned Russia on Sunday that if hunger-striking Kremlin critic Alexei Navalny dies in prison, it would face "consequences," as the opposition politician's team called for nationwide demonstrations to help save his life.

A day after Navalny's doctors warned that the Kremlin would be "kept accountable by the international community" if he died, US President Joe Biden's national security adviser said Washington had warned the Kremlin that if he died, it would be "held accountable by the international community."

On Sunday, France, Germany, and the European Union joined a rising international chorus of condemnation of Navalny's plight, and EU foreign ministers will meet on Monday to address the situation.

Concerns about Navalny's health have grown amid a new round of tensions between Moscow and the West over a slew of issues, including Russia's troop build-up on Ukraine's border, election meddling in the United States, and other ostensibly hostile activities.

On Sunday, Navalny's team called for nationwide protests on Wednesday evening, just hours before Putin was scheduled to deliver his state of the nation speech.

“Now is the time to take action. Navalny's right-hand man Leonid Volkov said on Facebook, "We are not only talking about Navalny's independence but his life."

Wednesday's rally, according to Volkov, may be a decisive fight against "pure evil" or Russia's last opposition rally for years.

“Call all your friends and go to the central squares,” wrote Volkov, who is in charge of Navalny's regional offices, adding that the protests should be large.

The Kremlin did not react immediately, but Andrei Kelin, the Russian ambassador in London, said Navalny "would not be able to die in prison."

Kelin told the BBC, "But I can tell that Mr. Navalny acts like a hooligan."

Authorities have increased their pressure on Navalny's supporters in recent months, detaining over 10,000 demonstrators during opposition rallies in January and February.

Russian prosecutors requested a court on Friday to mark Navalny's Anti-Corruption Foundation and his network of regional offices as "extremist" organizations, which would make them illegal in Russia and subject their members and supporters to jail time.

Navalny was apprehended in January after returning to Russia following a near-fatal poisoning attack that he claims was orchestrated by the Kremlin. The accusation is denied by the Kremlin.

In a penal colony near Pokrov, about 100 kilometers (60 miles) east of Moscow, the Putin critic is serving two and a half years on old embezzlement charges, which he claims are politically motivated.

On March 31, Navalny started a hunger strike to demand proper medical attention for his back pain and numbness in his legs and hands.

Navalny's doctors announced on Saturday that his health had steadily deteriorated and requested immediate access from prison authorities.

“Our patient could die at any moment,” cardiologist Yaroslav Ashikhmin said, citing Navalny's elevated potassium levels and recommending that he be transferred to intensive care.

A team of doctors, including Navalny's personal doctor, Anastasia Vasilyeva, attempted to see Navalny again on Sunday but were denied entry, according to a video.

On Saturday, Biden said Navalny's situation was "totally, totally unacceptable, totally inappropriate." On Sunday, US National Security Advisor Jake Sullivan said the Kremlin had been warned that "if Mr. Navalny dies, there will be repercussions."

Navalny's detention was described as "politically motivated" by EU foreign policy chief Josep Borrell, who added that "Russian authorities are responsible for Mr. Navalny's safety and health."

“We urgently demand that Alexei Navalny obtain appropriate medical care and access to doctors he trusts,” German Foreign Minister Heiko Maas said.

His French counterpart, Jean-Yves Le Drian, said the EU was keeping an eye on Navalny's case and cautioned that further EU sanctions against Russia could be imposed.

Washington imposed new sanctions on Moscow earlier this week in response to a major cyberattack, election meddling, and other activities.

Navalny's potassium levels in his blood were 7.1 mmol (millimole) per liter, which is substantially higher than the 6.0 level that normally necessitates immediate care.

On Saturday, spokeswoman Kira Yarmysh said, "Alexei is dying."

“It's just a matter of days in his condition.”