Have not tracked nerve agent source, admits UK defence lab

Scientists at the UK's Porton Down lab previously identified the poison as a Soviet-developed type of nerve agent known as Novichok. The British government has said the only plausible explanation was that it came from Russia and blamed Russia for the attack on the former double agent and his adult daughter.

Porton Down chief executive Gary Aitkenhead said Tuesday that scientists at the lab "have not verified the precise source, but we provided the scientific information to the government who have then used a number of other sources to piece together the conclusions that they have come to."

Aitkenhead told Sky News the attack with a highly toxic chemical weapon was "probably only within the capabilities of a state actor." At the same time, the lab's job is "to provide the scientific evidence that identifies what the particular nerve agent is ... but it's not our job to say where that was actually manufactured," he said.

Russian President Vladimir Putin quickly pointed at Aitkenhead's statement as evidence that British accusations of Russian involvement were unfounded. Moscow has fiercely denied being behind the March 4 attack.

"The speed at which the anti-Russian campaign was launched causes bewilderment," Putin said from Turkey, where he met with President Recep Tayyip Erdogan. Putin added that Russia will push for a thorough probe and expects the international chemical weapons watchdog to consider Russia's input.

"We want a thorough investigation. We would like to take part in it and expect to receive all the relevant materials," Putin said. He insisted the nerve agent that Britain said was used to attack former double agent Sergei Skripal and his daughter, Yulia, could have been produced by some 20 nations.