The EU said it holds Russia responsible for the health of Alexei Navalny, after doctors warned the condition of the Kremlin critic was rapidly deteriorating.
Josep Borrell, the EU’s foreign policy chief, also described the situation on the Russia-Ukraine border as “very dangerous”, amid a build-up of Russian troops there.
Mr Navalny, who is in a Russian jail, began a hunger strike on March 31, demanding treatment for back and leg pain.
He was moved to a prison hospital on Monday, although Russian authorities insisted his condition was “satisfactory” and said he was taking vitamin supplements as part of medical treatment.
He was arrested in Russia in January, after surviving a nerve agent poisoning he claims was ordered by the Kremlin.
“We make the Russian authorities responsible for the health situation of Mr Navalny,” Mr Borrell said, ahead of a video conference with EU foreign ministers where Russia will be top of the agenda.
Lithuania said its foreign minister Gabrielius Landsbergis would propose that the EU “take immediate measures” at the talks on Monday.
“If the international community does not respond, the regime’s opposition leader will be sent silently to his death,” Mr Landsbergis said.
Ukraine’s foreign minister Dmytro Kuleba briefed his EU counterparts on the tensions with Russia.
“I proposed a step-by-step plan on how to discourage Moscow from further escalation,” he tweeted.
“Key element: preparing a new set of sectoral sanctions. Individual ones are not sufficient anymore.”
German foreign minister Heiko Maas said “the good news is that Mr Navalny now finally appears to receive urgently necessary medical aid.
“We will follow very closely if this actually happens,” he added
Mr Borrell said Russia’s live fire exercises and deployment of troops on its border with Ukraine had made for a very dangerous situation.
“All in all, relations with Russia are not improving. On the contrary, the tension is increasing on different fronts.”
At the weekend, French President Emmanuel Macron said that while dialogue with Russia is essential, “clear red lines” carrying possible sanctions must also be drawn with Moscow over Ukraine.
Mr Kuleba has repeatedly asked for more Western backing, saying “words of support aren’t enough”.