Russian opposition leader Alexei Navalny has been sentenced to two years and eight months in a prison by a Moscow court.
The conviction is a landmark decision for Vladimir Putin's government, who have continued to pursue Navalny, even while he lay fighting for his life after being poisoned by Novichok, which critics believe was allegedly instigated by them.
Mr Navalny, who has accused the Russian president and his allies of stealing billions, was jailed for violating parole from a 2014 sentence for embezzlement, a case he has said was politically motivated.
The Kremlin’s decision to send him to prison came despite the threat of further street protests and international condemnation from the US government and other foreign leaders.
Navalny, who has already served a year under house arrest, becomes the most prominent political prisoner in Russia and is a significant verdict against one of Putin's rivals since the 2005 jailing of Mikhail Khodorkovsky.
His supporters called for an immediate protest, and hundreds gathered in central Moscow and St Petersburg despite a heavy police presence. More than 850 have been detained in Moscow alone, according to reports.
The US secretary of state, Anthony Blinken, said Washington was “deeply concerned” and reiterated calls for Navalny’s unconditional and immediate release, saying it would coordinate with allies to hold Russia accountable.
Boris Johnson described the ruling as “pure cowardice,” which failed to meet “the most basic standards of justice”.
“Alexey Navalny must be released immediately,” he wrote.
The German foreign minister, Heiko Maas, described it as a “bitter blow” to the rule of law in Russia.
Addressing the court before the sentencing, Mr Navalny, in a 16 minute speech said the case was being used to frighten the opposition.
"This is how it works: they send one to jail to intimidate millions."
“You can’t imprison the whole country,” he added.
More than 5,000 people were detained in nationwide protests this weekend and senior Navalny aides have been swept up in government raids.
On the Novichok chemical attack, he said: "Using the Federal Security Service of Russia, Putin attempted to commit murder. I'm not the only one - many know this already and many others will. And this is driving the thieving little man in the bunker crazy.
"No matter how much he tries to look like a geopolitician, he took offence at me because he will go down in history as a poisoner."
Mr Navalny returned to Russia on 17 January. It triggered mass protests in support of him.
The Kremlin has denied any involvement in the attack on him, and rejects the conclusion by Western experts that Novichok - a Russian chemical weapon - was used.
For years, the government has tried to intimidate and silence Navalny, holding him under house arrest, jailing his aides and imprisoning his brother for three-and-a-half years in 2014.