Vladimir Putin's most high-profile Russian critic was back in a Moscow court on Friday (February 5) for a slander trial.
Alexei Navalny is accused of slandering a World War Two veteran who took part in a promotional video last year.
The video supported reforms that allowed Putin to run for two more terms after 2024 if he wanted to.
Navalny called the people in the video "corrupt lackeys" and "traitors without a conscience."
Earlier this week, he was jailed for three years for parole violations - accusations he said were "trumped up."
Western governments have condemned that trial, which spurred talks of sanctions.
Russia, in turn, accused the West of hysteria.
The EU's top diplomat Josep Borrell was in Moscow on Friday.
"My visit coincided with arrest and sentencing of Alexei Navalny and the arrest of thousands of demonstrators. As you can expect I have conveyed to Mr. Lavrov our deep concern and reiterated our appeal to his release and a launch of an impartial investigation over his poisoning."
Since he was sentenced last week, widespread protests have been held across Russia in support of Navalny.
Thousands have been detained, according to a protest monitor.
Russian authorities said the demonstrations were broken up because they were illegal.
An associate of Navalny said on Thursday (February 4) his allies would postpone street protests for now - and would start them again in the spring and summer.
In the slander trial, the charge is punishable by up to two years in jail.
Navalny's lawyer has argued he cannot be sentenced because the alleged crime was committed before the law was changed to make it a jailable offense.