苏联神经毒剂与俄罗斯政客疾病有关

Novichok is a deadly nerve agent that left Russian opposition politician Alexei Navalny in a coma. It also nearly killed a former Russian spy and his daughter in 2018.

Novichok was the creation of a very secretive chemical weapons program when Russia was part of the Soviet Union. Here is a look at the nerve agent and its history.

How deadly is Novichok?

Novichok has been described as much deadlier than anything created by the United States. Just a few milligrams of the odorless liquid are enough to kill a person in a few minutes. The nerve agent could be watered down to the desired amount and added to food or drink. It also could be placed on clothing or other things the intended victim will touch.

In the attack on former Russian spy Sergei Skripal, a small amount was placed on the front door of his house in Salisbury, England. He and his daughter Yulia spent weeks at a local hospital in critical condition before recovering. A local woman later died after she found a bottle containing the nerve agent.

What does Russia say about Novichok poisonings?

Russia strongly denied British accusations over the poisoning of the Skripals. It accused Britain and other Western nations of using the poisoning to fuel an anti-Russian campaign.

German Chancellor Angela Merkel called Navalny's poisoning an attempted murder that aimed to silence the fiercest critic of Russian President Vladimir Putin.

Russia has demanded that Germany share all information leading to its announcement that Navalny was poisoned. Russia also has called for a joint investigation effort.

President Putin's spokesman, Dmitry Peskov, said Thursday that "there is no reason to accuse the Russian state" over the poisoning. He said that Russian doctors in Siberia found no evidence of poisoning.

Navalny was on a flight from Tomsk, in Siberia, to Moscow when he collapsed. The flight returned and Navalny was taken to a hospital in Omsk, also in Siberia.

Sergei Naryshkin is the head of the Russian Foreign Intelligence Service. He said it is possible that Navalny's poisoning was carried out by Western intelligence agencies as a provocation.

When was Novichok designed?

The Soviet program to design a new generation of chemical weapons was launched in the 1970s to answer the latest U.S. chemical weapons. The Soviets created several deadly poisons, some no less than military-grade nerve agents.

The Soviet leadership later lost interest in chemical weapons. Novichok-class nerve agents were made only in small amounts for use in laboratories. Vladimir Uglev was a top scientist in the program. He has estimated about 100 kilograms were made.

Is it possible to identify where Novichok was made?

Russian experts who have worked on the Novichok class of agents have warned it may never be possible to know where the nerve agent came from. To identify which lab manufactured a given batch of Novichok, investigators need another sample from the same batch -- an impossible requirement.

Could it fall into the wrong hands?

The main Soviet research center that created the Novichok nerve agents was in Shikhany, a town in southwestern Russia. It was one of the "closed cities" controlled by Soviet security forces. The research center also had chemical weapons storage areas and a military firing range. Nerve agents were tested there during Soviet rule.

Some Novichok-related research also was done at a research center in Moscow. It shared samples with other labs across the Soviet Union.

When the Soviet Union collapsed, the United States attempted to oversee the destruction of chemical weapons in Russia. Scientists involved in the program said it was possible that lab workers may have sold the nerve agents during the economic and political unrest of the 1990s.

Russia said in 2017 it completed the destruction of 40,000 metric tons of chemical weapons left over from the Soviet period. At first, the Novichok nerve agents were not listed in the Chemical Weapons Convention, an international document that banned chemical weapons.

Last year, however, they were added to the list of chemicals that require special verification measures under the treaty's rules.

I'm Susan Shand.

The Associated Press reported this story. Susan Shand adapted it for Learning English. George Grow was the editor.