Prominent Kremlin critic Vladimir Kara-Murza was sentenced Monday by a Moscow court to 25 years in prison for treason.

The opposition activist has criticized Russia's war against Ukraine and is known as one of the fiercest critics of Russian President Vladimir Putin.  

Prosecutors had requested the long sentence at the beginning of April, writes the BBC.

According to Kara-Murza's lawyer, Maria Eismont, the politician is in bad health.

The Russian-British former journalist and politician is the latest of several opponents of Putin to be arrested or forced to leave Russia.

He has denied all the charges.

Last week, he said in a statement: "I stand by every word I've said... Not only do I regret nothing, I'm proud of it. I know the day will come when the darkness that has engulfed the country our society will be cleansed... Our society will open its eyes and tremble when it realizes what crimes have been committed in its name".

Kara-Murza's 25-year sentence was the maximum sought by prosecutors and is the longest sentence an opposition figure has received since the start of the war in Ukraine.

It only took a few minutes for the judge to rule on his case - a process that can sometimes take a long time in Russian courts.

The harsh punishment is a sign that in today's Russia the authorities are determined not only to silence critics, but also to neutralize anything or anyone they believe represents a threat to the political system.

The BBC was not allowed into the court and only a handful of journalists from Russian state media were given access, along with the defendant's mother and lawyer.

Instead, journalists and foreign ambassadors crowded into a separate room to watch the proceedings on two television screens.

Speaking outside court after the sentencing, Kara-Murza's lawyer, Maria Eismon, said the harsh sentence was "terrible" but also a "high praise" for her client's work.

"When [Mr. Kara-Murza] heard that it was 25 years, he said: my self-esteem even increased; I realized that I had done everything right!", she said.

Last year, Kara-Murza won the "Vaclav Havel" human rights award.

He dedicated the award to all those in Russia who are against the war in Ukraine.