Alexei Navalny denounced Russian President Vladimir Putin as a "naked, thieving king" in a courtroom video link from prison, in his first public appearance since ending a hunger strike last week.
The opposition leader's remarks on a blurry video piped into a Moscow courtroom came amid new legal pressure on Mr Navalny and his movement.
Allies said he faced new criminal charges and they had been forced to disband his network of regional campaign offices, which the authorities are seeking to ban as "extremist".
Mr Navalny, his head shaven, said he had been taken to a bathhouse to look "decent" for the hearing.
April 29, 2021, Russian opposition leader Alexei Navalny is seen on TV screens gesturing during a hearing on his charges for defamation in Moscow, Russia. Source: Babuskinsky District Court
"I looked in the mirror. Of course, I'm just a dreadful skeleton," he said, adding that he now weighed 72kg, the same weight as when he was at school.
Later in the appeal hearing against a guilty verdict on a charge of defaming a World War Two veteran, Mr Navalny, 44, went on the attack against Mr Putin and the Russian justice system. At one point he interrupted the judge, and was reprimanded.
"I want to tell the dear court that your king is naked," he said of Mr Putin. "Millions of people are already shouting about it, because it is obvious... His crown is hanging and slipping."
The court dismissed the lawyers' appeal against Navalny's conviction in the veteran slander case. Source: BABUSHKINSKY DISTRICT COURT
Reiterating allegations of corruption that the Kremlin denies, he said: "Your naked, thieving king wants to continue to rule until the end ... Another 10 years will come, a stolen decade will come".
A separate court is considering whether to declare Mr Navalny's Anti-Corruption Foundation (FBK) and his network of regional campaign offices "extremist", which would give authorities the power to jail activists and freeze bank accounts.
"Maintaining the work of Mr Navalny's network of headquarters in its current form is impossible: it would immediately ... lead to criminal sentences for those who work in the headquarters, who collaborate with them and for those who help them," Leonid Volkov, one of Mr Navalny's close allies, said in a YouTube video.
Mr Volkov said many of the offices would try to function as independent regional bodies with their own leaders.
Mr Navalny's allies also said a new criminal case had been opened against him for allegedly setting up a non-profit organisation that infringed on the rights of citizens. This could not immediately be confirmed.
Alexei Navalny behind the glass of a cage in the Babuskinsky District Court in Moscow, Feb. 20, 2021. Source: AP
Mr Navalny is serving a two to two-and-a-half year jail sentence for parole violations on an earlier embezzlement conviction that he says was politically motivated.
Last year, he survived an attack with a nerve agent. After recovering in Germany, he was arrested on his return to Russia in January and sentenced the following month.
He declared his hunger strike in prison on 31 March to demand better medical care for leg and back pain.
On 23 April, he said he would start ending it after getting more medical care. Russia has said he is receiving the same treatment as any other prisoner and accused him of exaggerating his health needs for publicity.
