Princeton (United States) (AFP) - The Russian chemist who first revealed the existence of "Novichok" nerve agents says only the Russians can be behind the weapon's use in Britain against a former spy and his daughter.

Vil Mirzayanov, 83, came to the United States in 1995 after 30 years of working for the State Scientific Research Institute of Organic Chemistry and Technology, or GNIIOKhT.

It was he who in the early 1990s revealed the existence of that class of ultra-powerful nerve agents.

He did so first in the Russian media as it opened up with the collapse of the Soviet Union, and later, with chemical formulas at hand, in his book "State Secrets," published in 2007.

Former Russian agent Sergei Skripal and his daughter Yulia were found slumped on a bench in the English city of Salisbury on March 4. Britain says it is "highly likely" that Moscow was to blame for the nerve agent attack.

Mirzayanov, speaking at his home in Princeton, New Jersey, said he is convinced Russia carried it out as a way of intimidating opponents of President Vladimir Putin.

"Only the Russians" developed this class of nerve agents, said the chemist. "They kept it and are still keeping it in secrecy."

The only other possibility, he said, would be that someone used the formulas in his book to make such a weapon.

- 'Dangerous for the Kremlin' -

He said that the Russians could argue that maybe someone had synthesized them "and they could make me guilty!"

This is the first time the nerve agents, which took 15 years to develop and were tested on animals, have been used to try to kill somebody, Mirzayanov said.

Why now? Mirzayanov said he believes the Kremlin wants to intimidate people, such as enemies of Putin.

For instance, he hypothesized, suppose someone leaves Russia with material that would compromise President Donald Trump in the US probe into whether his 2016 election campaign colluded with Russia in its alleged drive to help him beat Hillary Clinton.

"It's very dangerous for the Kremlin because it is a plot against America," said the chemist. "So they threaten this person, and they say, 'look what happened to Skripal. The same could happen to you.'"

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Mirzayanov said Skripal could no longer cause Russia any problems but the Kremlin could have killed him anyway, and in a cruel fashion, just to intimidate potential opponents.

- No cure -

An attack with Novichok agents, which are 10 times stronger than VX, is excruciating and has no cure, he added.

He said half a gram is enough to kill a person who weighs 50 kilos (110 pounds).

Someone exposed to it first has their vision go blurry, and if no antidote is applied are then hit with violent convulsions and can no longer breathe.

"I have seen the effect on animals -- rabbits, dogs. It is awful," he said.

Even if they do not die, Skripal and his daughter will suffer for the rest of their lives, he predicted.

The nerve agents are easy to administer because they are binary, meaning they result from the mix of two substances which on their own are harmless.

So these two parts can be transported with no risk, then blended to make the weapon in a spray gun.

Mirzayanov said that as awful as it has been, the attack in Britain might lead to something good: the UK and other Western countries insisting on Novichok agents being registered in the Convention on the Prohibition of Chemical Weapons, as he has been urging for more than 20 years.

Had these weapons been placed under control the Salisbury attack might not have happened, he said.

Now that Mirzayanov is speaking openly about Novichok, his friends on Facebook and elsewhere are urging him to be careful, lest the Russians seek reprisal against him.

"But I have lived for quite a long time. They cannot stop me. I will work until the end to have Novichok placed under international control," he said.