(CNN) The UK has assessed that the brazenness of the attacks that killed one Briton and sickened a former Russian spy and his daughter — including the amount of nerve agent used — point to approval by Russian President Vladimir Putin himself, two officials familiar with the matter told CNN.

"It's above the GRU leadership," is as far as a British official would go when asked to confirm CNN's reporting that Putin authorized the attack. "What that actually means, we can have a good guess."

British officials have warned allies that Russian intelligence agents risked killing thousands when they smuggled a perfume bottle packed with the deadly nerve agent Novichok into the UK to try to assassinate Sergei Skripal, a former Russian agent, according to two European intelligence officials.

The poison, contained in a fake Nina Ricci perfume bottle, was enough to kill "thousands and thousands of people," according to the intelligence officials, speaking anonymously in order to discuss sensitive briefings. "Just the amount on the head of a pin could kill," one of the officials explained.

"It could have been carried in by the Russians who carried out the operation," on commercial aircraft, though it also could have been smuggled in a diplomatic pouch, they said.