Moscow (CNN) Opposition activists in Russia are accusing the Kremlin of creating an "atmosphere of impunity" amid a growing row over a threatening video posted online.

The video, which appeared on the Instagram account of the pro-Kremlin Chechen President Ramzan Kadyrov , shows two prominent Russian opposition figures in the cross-hairs of a sniper's gun sights.

Activists have called it "incitement to murder."

One of those in the video -- since removed by Instagram -- Vladimir Kara-Murza, of the Open Russia Foundation, told CNN the political opposition in Russia is now "seeing open threats from Mr. Kadyrov and his henchmen".

"The Chechen president," Kara-Murza told CNN, "has not even been formally questioned by investigators".

In another recent example of what activists say is intimidation, a close ally of Kadyrov posted a photograph of the Chechen leader handling an aggressive dog, named "Tarzan".

"His fangs are itching to bite important opposition figures," the post said. "We can barely restrain him.

The high mortality rate of the Kremlin's opponents

But it's not just threats of bullets and dog bites Russia's beleaguered opposition now has to contend with.

VIadimir Kara-Murza, 34, is only just back on his feet after a mysterious poisoning in May that nearly killed him.

"I fell into a coma, all of my major organs began failing, one after another. It was the kidneys first, then the lungs, the heart, the liver," he told CNN.

Doctors say they have yet to determine the cause of the poisoning. But Kara-Murza and his family say they believe it is was a "sophisticated substance" of a kind the Russian FSB -- successor to the KGB -- may have access to.

He has now formally requested an investigation into what he believes was a politically motivated attack.

For its part, the Kremlin denies any involvement in the alleged poisoning, which has obvious parallels with the killing of former Russian agent Alexander Litvinenko in London.

A British public inquiry into that 2006 poisoning found two former Russian agents responsible for carrying out the poisoning with the radioactive isotope Polonium-210. Its final report concluded that Russian President Vladimir Putin was "probably" aware of the operation.

The Russian Foreign Ministry dismissed the UK inquiry as politically motivated.

In recent years there has certainly been a very high mortality rate among prominent opponents of the Russian leadership, and activists say they are increasingly concerned for their safety.

Not everyone's laughing at Putin cartoons

But the Kremlin seems to be basking in -- or making light of -- its reputation for ruthlessness.

A series of bizarre cartoons was recently released by Russia's ruling party showing Putin executing his opponents in inventive and comical ways.

In each short animation, Putin is shown meeting with a public official, hearing them talk, and then witnessing his death.

In one scene, an environmental minister from the Republic of Karelia is hacked to death by an axe-wielding tree.

In another, Putin's magic watch button causes a drone to vaporize his opponent with a laser.

It's meant to be a lighthearted take on Putin's fight against official corruption. But in a country where real opposition figures have been gunned down on the street, not everyone is laughing.

The recent sniper-sight video controversy comes just a few weeks before the one-year anniversary of the killing of Boris Nemtsov , one of Russia's most high-profile opposition leaders.

He was gunned down near the Kremlin in February 2015 as he walked home from a restaurant with his girlfriend.