A Russian poet who criticised his country's invasion of Ukraine in a four-line poem has been sentenced to seven years jail, the OVD-Info rights group said Thursday.

Alexander Byvshev, 51, allegedly wrote the poem on his Facebook page in March 2022. "Rockets are hitting Ukraine. The Kremlin has rejected conscience and morality," it said.

The last line asks the military why there is no Russian "Stauffenberg", a reference to German army officer Claus von Stauffenberg who tried to assassinate Adolf Hitler.

Prosecutors took this to be a veiled death threat against Russian President Vladimir Putin and charged Byvshev with "calls for terrorism", OVD-Info said.

They also charged him with spreading "fake" information about the Russian army, after he posted an image of a Ukrainian village in ruins on social media.

Byvshev, from the western region of Oryol, was found guilty on both counts and sentenced to seven years imprisonment by a Moscow court on March 19, according to OVD-Info.

The Kremlin made opposing the war a crime shortly after it sent troops into Ukraine in February 2022, and thousands have been detained for simple acts of protest.

Since launching its offensive in Ukraine, Moscow has waged an unprecedented crackdown on dissent that rights groups have likened to the Soviet-era mass repression.

On Wednesday, a Saint Petersburg court jailed a Russian filmmaker for three years after he made anti-war posts on his social media shortly after the war began.