On the television screen, jailed opposition leader Alexei Navalny peered through a barred window, laughing and cracking jokes about his depleting funds and the judge's salary.

The 47-year-old appeared well and cheerful as he gave testimony by videolink on Thursday. The camera panned away to show the court officials grinning along with him, enjoying the banter.

A day later, Russia's prison service said he had died after collapsing and losing consciousness at the penal colony north of the Arctic Circle where he was serving a long jail term.

The man who was by far Russia's most famous opposition leader rose to prominence more than a decade ago by lampooning the elite class around President Vladimir Putin.

His trademark humour was back on show on Thursday when he made his last appearance, dressed in black prison uniform.

"Your Honour, I will send you my personal account number so that you can use your huge salary as a federal judge to 'warm up' my personal account, because I am running out of money," he said.

The online news outlet SOTA reported that the court session was convened after an "argument" with a prison officer who tried to confiscate Navalny's pen.

Navalny wrote later on Thursday that he had been given 15 days in solitary confinement.

Since first being jailed in Jan. 2021, Navalny had been in and out of solitary confinement, which is often used to punish rulebreakers in the Russian prison system.

After the hearing, Navalny took to social media. "The Yamal prison decided to break Vladimir's record of fawning and pleasing the Moscow authorities. They just gave me 15 days in solitary confinement," he wrote on X.

"This is the fourth solitary confinement spell in less than 2 months that I have been with them," he added.

It was the last such message he wrote. (Reporting by Felix Light; Editing by Andrew Heavens)