MOSCOW • Poison has been a favoured tool of Russian intelligence agencies for more than a century. And critics of the Kremlin and independent analysts say the weapon remains in use today.
While countries, including the United States and Israel, have targeted killing programmes, they are strictly limited to counter-terrorism efforts. Russia, by contrast, has been accused of targeting a wide variety of opponents both at home and abroad.
The Soviet Union operated a secret laboratory to research tasteless, untraceable poisons that were tested on condemned prisoners, defectors have said.
After a series of assassinations of dissidents, journalists, defectors and opposition leaders in Russia and abroad over the past two decades, researchers have concluded that the post-Soviet government has turned to its poison arsenal as a preferred weapon.
Substances identified or suspected in poisonings blamed on the Russian government include radioactive polonium-210; heavy metals; gelsemium, a rare Himalayan plant toxin; and Novichuk, a military nerve agent lethal to the touch.
Lacing a meal or cup of tea with poison is simple and requires no special training, one-time KGB colonel and former opposition parliamentarian Gennadi Gudkov said.
"It is easy, and easy to cover your tracks. Any person can use poison," he said, adding that poisons can be intended either to kill or to incapacitate a person with a long, unpleasant illness.
Dr Yaroslav Ashikhmin, the personal doctor of Russian opposition politician Alexei Navalny - who is now in coma following a sudden illness shortly after drinking a cup of tea at an airport cafe last week - said he had not seen Mr Navalny since the illness began, so he could not say if poison was the cause.
But he added: "It looks like it."