Intelligence officials in the U.K. have reportedly concluded privately that an assassination attempt carried out against a former Russian spy living in Britain could only have been undertaken with the approval of Russian President Vladimir Putin Vladimir Vladimirovich PutinPutin nominated for Nobel Peace Prize Navalny released from hospital after suspected poisoning Ex-Trump national security adviser says US leaders 'making it easy for Putin' to meddle MORE.

CNN reports that British officials have determined that the amount of nerve agent believed to have been possessed by two Russian intelligence agents involved in the crime points to the likelihood of Putin signing off on the killing himself.

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"Thousands and thousands of people" could have been killed with the amount of Novichok contained in a fake perfume bottle used in the crime, according to British intelligence officials familiar with the case speaking anonymously.

"Just the amount on the head of a pin could kill," due to the toxicity of the poison, one official added.

Neither Sergei Skripal, the intended target of the attack, nor his daughter was killed in the attack, but both were seriously injured and another woman who came in contact with the bottle later died.

When asked to comment publicly on the CNN report, one British official told the network only that the U.K. had determined the killing to have been ordered "above the GRU leadership," referring to Russia's intelligence service.

"What that actually means, we can have a good guess," the official added.

Former CIA officer John Sipher added to CNN that the amount of nerve agent carried by Russian intelligence agents pointed clearly to Putin's involvement.

"You don't jump on a plane with enough doses to kill thousands ... without your boss knowing about it," he said, according to the network. "Because it was a GRU officer being targeted, even if they pulled it off perfectly, it would be blamed on Russia."

The attempted assassination of the Skripals evolved into an international incident for Russia, which has battled claims from the U.K. and U.S. that it was involved in the incident. Russian officials have accused their British counterparts of refusing to listen to explanations for the incident and using it to inflame international tensions.

"I see that some of your colleagues are pushing the theory that Mr. Skripal is almost a human-rights activist," Putin himself said at a recent energy summit, according to CNN. "He's just a spy. A traitor to the Motherland. There's such a thing as a traitor to the Motherland. He's one of them. He's just a scumbag, that's all."