Russian authorities have launched a manhunt by "effectively arming the country's criminal justice system" to prosecute anti-war protesters and influential critics who have voiced opposition to Russia's invasion of Ukraine, Amnesty International said.

"The persecution of those who opposed Vladimir Putin's invasion of Ukraine goes well beyond previous efforts to stifle protesters and activists," said Marie Struthers, Eastern Europe and Central Asia director at Amnesty International.

She added that those "who are caught criticizing the war face an unreasonable number of arbitrary charges just for speaking out".

The human rights official indicated that they are not only accused of "defaming" the armed forces, but "also with slander, fraud, or accusations of terrorism."

Amnesty International quoted the Russian human rights organization Agora as saying that just one month after the Russian invasion of Ukraine, at least 60 criminal cases were filed due to peaceful protests against the war or public criticism of the Russian authorities.

At least 46 people faced criminal charges, of whom 9 were held and 3 were under house arrest, and were charged with a myriad of "offences", including insulting government officials, slander, inciting extremist activities, inciting mass riots, and hatred fraud, and desecration of burial sites, according to the Agora.

At least 10 of these cases saw critics investigated under a new law for "defaming" the Russian armed forces, a charge punishable under new Russian law with up to 10 years in prison or 15 years if the comments cause "serious consequences".