Jailed Kremlin critic Alexei Navalny's anti-corruption group vowed Thursday to fight on after a court called it an "extremist" organisation and ordered its closure.
EU members and other western countries were quick to condemn Wednesday's late-night ruling, but Russian officials described Navalny as an agent collaborating with Washington.
The court decision, before parliamentary elections in September, was the latest move in a campaign against critics of the Kremlin.
Some of its most vocal opponents have fled the country and some activist groups and independent media have closed.
The ruling bans Navalny's Anti-Corruption Foundation and a network of regional offices from operating and, under a recently passed law, prevents those associated with the groups from running in elections.
The Foundation was defiant, saying on Twitter on Thursday morning: "We woke up, smiled with destructive intent and knowing that we are a 'danger to society' will continue to fight corruption."
What it will be able to do is unclear after the ruling, which followed a 12-hour hearing behind closed doors.
Navalny's key allies still in Russia are under close law enforcement supervision, some under house arrest, and other prominent aides have gone into exile.
He was jailed for more than two and a half years in February after he returned from Germany where he had been convalescing after a poisoning attack that he blamed on the Kremlin.
Russia's most prominent opposition leader, who is in a penal colony outside Moscow, acknowledged supporters would now have to change their strategy.
The ruling came at a difficult time for Russia's embattled opposition, which hoped to make a dent in the Kremlin's monopoly on political life during parliamentary elections in September.
"But we will not retreat from our goals and ideas. This is our country and we have no other," Navalny, 45, said on Instagram.
The EU condemned the court ruling as the latest effort to "suppress" the opposition.
"It is an unfounded decision that confirms a negative pattern of a systematic crackdown on human rights and freedoms which are enshrined in the Russian constitution," EU foreign policy chief Josep Borrell said.
Amnesty International said the ruling placed "tens of thousands of Navalny's supporters at risk of prosecution".
"This is one of the Kremlin's most cynical and brazen attempts so far to crack down on the rights to freedom of expression and association," the rights group said.
The committee of ministers of pan-European rights body the Council of Europe said it strongly urged Russia to "immediately" release Navalny.
UK Foreign Secretary Dominic Raab had described the ruling as "perverse" and "Kafka-esque", while the US called on Moscow to end the crackdown and release Navalny.
US President Joe Biden has promised to raise the issue of human rights with Russian President Vladimir Putin when the two meet next week in Geneva.
The spokeswoman for Russia's Foreign Ministry said the international outcry suggested Navalny was working with foreign governments.
"They show such political zeal because it touches those whom they supervised, those whom they supported politically and in other ways," Maria Zakharova said.
Russian authorities have accused the opposition of working for and receiving funding from foreign interests.
Prosecutors in April requested that Navalny's organisations be given the "extremist" designation, saying they were plotting an uprising with support from the West.
Announcing the decision on Wednesday, a representative of the prosecutors said Navalny's groups had "incited hatred and enmity against government officials, but also committed extremist actions".
His network of regional offices had promoted his "smart voting" campaign, which encouraged voters to cast ballots for candidates most likely to unseat Kremlin-friendly incumbents.
Leonid Volkov, a close ally of Navalny who used to run the nationwide network of offices, said on Thursday that this work would continue.
"Although Navalny's headquarters no longer exist, we, Navalny's team, are still working on smart voting," he said in a YouTube video.
"Our task in the autumn elections to the State Duma is to win as many mandates as possible from United Russia," he said, referring to the Kremlin-aligned ruling party.
But legislation signed by Mr Putin this month bars employees and even supporters of "extremist" groups from running in elections, paving the way for a clear sweep by Kremlin-backed candidates.
The FBK, which has published investigations into the wealth of Russia's elites, independently investigated Navalny's poisoning and concluded that attack was carried out by the FSB security agency.
On Thursday, Navalny's allies said they gained access to his medical documents from a Siberian hospital. where he was first taken after his plane made an emergency landing, which showed symptoms consistent with a diagnosis of poisoning.
Political analyst Valery Solovei said Wednesday's ruling carried serious implications for many Russians.
"The most dangerous aspect of this decision is that it is retroactive," he said, noting that even regular Russians who visited Navalny's website in recent years or donated could be implicated.
"This is an indefinitely wide range of people."
