Russia has a problem and that problem is Vladimir Putin. It's unfortunate. Without Putin, America and Russia could be best friends and that would be a good thing.

Yulia, the daughter of Sergei Skripal

(CNN) British authorities examining the poisoning of former Russian spy Sergei Skripal believe the daring placement of the nerve agent on his door shows a sophistication that likely had the approval of the Kremlin, a source briefed on the investigation has confirmed to CNN.

Skripal, 66, and his daughter Yulia, 33, were poisoned on March 4 after being exposed to what the British government says was a military-grade nerve agent.

British officials believe an attack of this type could only be carried out by a person (or more than one person) with key training involving Novichok, the substance used in the attack.

There are doubts that rogue agents could have carried out the attack without approval from the top levels of Russian government.