EU foreign policy chief Josep Borrell said on Monday the bloc holds Russia "responsible" for the health of Kremlin critic Alexei Navalny, as EU foreign ministers held virtual talks on soaring tensions with Moscow.
The United States has warned the Kremlin of "consequences" if President Vladimir Putin's major domestic opponent - who is currently on hunger strike - dies in prison after doctors warned at the weekend he could pass away at "any minute".
Fears over the health of Navalny come amid major anxieties in the 27-nation European Union over a buildup of Russian troops along the border with Ukraine and a spiralling diplomatic row between Moscow and EU member state the Czech Republic.
Borrell said Navalny's condition was "very worrisome" and repeated a call for immediate access to be granted for medical professionals he trusts.
"We make the Russian authority responsible for the health situation of Mr Navalny," he said.
Lithuania said its Foreign Minister Gabrielius Landsbergis would propose that the EU "take immediate measures" at the video talks of the bloc's top diplomats Monday.
"If the international community does not respond, the regime's opposition leader will be sent silently to his death," Landsbergis said.
Navalny, 44, was arrested in Russia in January after returning from a near-fatal nerve agent poisoning he says was carried out by Moscow -- accusations denied by Putin's administration.
Sentenced to two and a half years in prison for embezzlement, he began a hunger strike on March 31 demanding medical treatment for back pain and numbness to his hands and legs.
The EU in October sanctioned six Russian officials over the Novichok nerve agent attempt and in February sanctioned another four individuals over Navalny's arrest and sentencing.
France's Foreign Minister Jean-Yves Le Drian said Sunday those sanctions could be expanded.
Navalny's supporters have called for a major protest across Russia on Wednesday to demand his release, hours after a state-of-the-nation address by Putin.
Ukraine, Czech tensions
EU foreign ministers will hold talks with Kiev's top diplomat at the meeting over a major military buildup by Russia along Ukraine's borders amid concerns over an escalation in the country's long-simmering conflict.
Borrell described the situation as "very dangerous" and called on Moscow to withdraw its troops from along the frontier.
Kiev has been battling Russian-backed separatists in eastern Ukraine since 2014 and clashes intensified early this year, effectively shredding a ceasefire agreed on last July.
Faced with the largest deployment of Russian troops on Ukraine's borders since 2014, President Volodymyr Zelensky has requested more help from the West.
EU foreign ministers are also set to be briefed on spiralling tensions between the Czech Republic and Russia.
Moscow on Sunday ordered out 20 Czech diplomats, a day after Prague announced it was expelling 18 Russian diplomats identified as secret agents of the SVR and GRU security services.
Czech authorities accused them of involvement in a deadly 2014 explosion on its soil at a military ammunition warehouse that killed two people.
Czech police said they were seeking two Russians in connection with the explosion and that the pair carried passports used by suspects in the poisoning of former Russian double agent Sergei Skripal in Britain in 2018.
The two Russians were identified as Alexander Mishkin and Anatoly Chepigov based on video footage from the site and photos published after the Skripal attack, according to Czech media.