A Saint Petersburg court on Wednesday handed jail terms of up to 12 years to six activists of the anti-war youth movement Vesna, the latest sentences in the Kremlin's campaign to silence critics.

Since launching its full-scale military assault on Ukraine in 2022 Moscow has suppressed opposition to the war and massively ramped up efforts to stifle criticism of Russian President Vladimir Putin.

Vesna, which means "spring" in Russian, was founded in Putin's hometown of Saint Petersburg in 2013 and later expanded into several other cities.

It was labelled extremist and a foreign agent in 2022.

The activists -- Anna Arkhipova, Yevgeny Zateyev, Valentin Khoroshenin, Yan Ksenzhepolsky, Vasily Neustroyev and Pavel Sinelnikov, aged from 24 to 30 -- were all arrested in June 2023, accused of "extremism" and spreading "false information" about the Russian army.

Moscow has used the charges widely over the last four years to target opponents of the Kremlin and the war.

Arkhipova was sent to a penal colony for 12 years, the harshest punishment among the group, with Ksenzhepolsky and Neustroyev jailed respectively to 11 and 10 years.

Cries of "Shame!" were heard in the court after the verdict was delivered, an AFP journalist reported.

One woman, who spoke only identified herself as Nika, said she came to court to support Zateyev.

"He's lucky, so to speak: six years isn't bad. He's been in prison for a long time, and it looks like he'll be out in about two years. I couldn't hope for more," she told AFP.

Zateyev's wife Lina, also present in court, slammed the sentences.

"We're happy for Zhenya, but the sentences for Anya, Yan, and Vasya are monstrous... I hope that someday those guilty of this repression will be punished," she told AFP, using the diminutive versions of the defendants' first names.

All the activists are recognised as political prisoners by the human rights organisation Memorial, which is also banned in Russia.

"My motivation is simple: I am against the war. I want the best possible future for Russia," Arkhipova, 28, said in her final statement in court in February, the independent Mediazona outlet reported.