(Bloomberg) -- The U.S. warned Russia of “consequences” if jailed opposition leader Alexey Navalny dies, deepening the conflict over the dissident who has already survived an alleged assassination attempt and is now engaged in the third week of a hunger strike.Navalny’s supporters on Sunday called for demonstrations across Russia on April 21, to coincide with President Vladimir Putin’s state-of-the-nation address. Putin’s most outspoken critic has been imprisoned since March 11 at the notorious IK-2 prison camp about 100 kilometers (60 miles) from Moscow for breaking parole rules. He’d gone to Germany to recover from a near-fatal chemical poisoning in Siberia that he and Western governments blamed on the Kremlin. Russian authorities deny any involvement.“We have communicated to the Russian government...they will be held accountable by the international community,” U.S. National Security Adviser Jake Sullivan said on CNN’s “State of the Union” on Sunday.“We are looking at a variety of different costs that we would impose, and I’m not going to telegraph that publicly at this point. But we have communicated that there will be consequences if Mr. Navalny dies,” Sullivan said. Separately, Ned Price, spokesman for the U.S. State Department, called in a tweet for Russian authorities to immediately provide Navalny with access to “necessary medical care,” while European Commission President Ursula von der Leyen called for the prisoner’s “immediate and unconditional release.” Navalny spokeswoman Kira Yarmysh said Saturday that he might die in a “matter of days.” His doctor, Anastasia Vasilieva, posted a copy of his blood-test results showing what she said were “critical” levels of potassium. “This signifies kidney failure, which can lead at any time to a severe disruption to his heartbeat” including the possibility of heart failure, she said on Twitter.After complaining of acute back and leg pain, Navalny began the hunger strike on March 31 to demand specialist care from doctors outside the prison system. In a post on his Instagram account Friday, Navalny’s allies reported that a prison official had warned him that a blood test indicated a “serious deterioration” in his health and that he would be force-fed if he didn’t end the protest.U.S. SanctionsPresident Joe Biden on Thursday ordered a raft of new sanctions against Russia, including restrictions on buying new sovereign debt, in response to allegations that Moscow was behind a hack on SolarWinds Corp. and interfered with last year’s U.S. election.Yet the moves were calibrated to punish the Kremlin for past behavior while keeping relations from deteriorating further, especially as tensions grow over a Russian military build-up near Ukraine. Biden has offered to meet Putin later this year, an invitation Russia said it responded to “positively.”At the same time, Navalny’s accelerating health crisis has sparked growing criticism in Western capitals.Biden was asked about Navalny’s condition on Saturday. “It’s totally, totally unfair,” he told reporters in brief remarks. Navalny’s fate is in Putin’s hands, French Foreign Minister Jean-Yves Le Drian said on Sunday. The Russian opposition leader’s health is a matter of “great concern,” German Foreign Minister Heiko Maas told the daily Bild, adding that Berlin “urgently” demands he receive adequate medical care. The European Union’s foreign policy chief Josep Borrell said in a statement that the 27-nation bloc was “deeply concerned” about reports of Navalny’s deteriorating state.Russia’s Federal Penitentiary Service didn’t respond to requests for comment. Officials have said previously that Navalny has received all necessary medical attention.Biden pressed Putin in a phone call on Tuesday about the poisoning of the opposition leader, which U.S. intelligence has publicly blamed on Russia’s Federal Security Service. German Chancellor Angela Merkel and French President Emmanuel Macron also quizzed Putin about Navalny in a March 30 phone call.Asked about the Russian threat to Ukraine in an interview with CBS’s Face the Nation, Macron said that warnings of “red lines” have to be followed up with action. “It’s a failure of our collective credibility vis-à-vis Russia,” he said.Dozens of public figures including five Nobel Literature Prize winners urged Putin in an open letter Friday to ensure that Navalny immediately receives medical treatment. So far, Russia has brushed aside all Western criticism of the case and Kremlin officials refuse even to mention Navalny by name.Even as his condition deteriorates, Russian prosecutors stepped up a crackdown Friday by asking a Moscow court to declare Navalny’s Anti-Corruption Foundation and his Moscow campaign headquarters to be extremist organizations. The opposition group warned that the designation could subject all of its staff and volunteers to criminal prosecution and imprisonment.More than 460,000 people have pledged anonymously to take part in new demonstrations calling for his release, according to a tally on Navalny’s website. Organizers on Sunday abandoned their goal of collecting half a million signatures to schedule a new protest, saying they could no longer wait, and called for the nationwide rallies instead.(Updates with Price, von der Leyen in fifth paragraph)For more articles like this, please visit us at bloomberg.comSubscribe now to stay ahead with the most trusted business news source.©2021 Bloomberg L.P.